Semiconductor device and a manufacturing method thereof

ABSTRACT

A lamination pattern having a control gate electrode, a first insulation film thereover, and a second insulation film thereover is formed over a semiconductor substrate. A memory gate electrode is formed adjacent to the lamination pattern. A gate insulation film is formed between the control gate and the semiconductor substrate. A fourth insulation film, including a lamination film of a silicon oxide film, a silicon nitride film, and another silicon oxide film, is formed between the memory gate electrode and the semiconductor substrate and between the lamination pattern and the memory gate electrode. At the sidewall on the side of the lamination pattern adjacent to the memory gate electrode, the first insulation film is retreated from the control gate electrode and the second insulation film, and the upper end corner portion of the control gate electrode is rounded.

CROSS-REFERENCE TO RELATED APPLICATIONS

The disclosure of Japanese Patent Application No. 2009-267029 filed onNov. 25, 2009 including the specification, drawings and abstract isincorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

The present invention relates to a semiconductor device and amanufacturing method thereof. More particularly, it relates to atechnology effectively applicable to a semiconductor device having anonvolatile memory and a manufacturing method thereof.

As electrically writable/erasable nonvolatile semiconductor storagedevices, EEPROMs (Electrically Erasable and Programmable Read OnlyMemories) have been widely used. The storage devices (memories) typifiedby currently and widely used flash memories have conductive floatinggate electrodes surrounded by an oxide film and trapping insulationfilms under gate electrodes of MISFETs. The storage devices use chargestorage states at the floating gates and the trapping insulation film asstorage information, and read out the information as a threshold valueof each transistor. The trapping insulation film denotes an insulationfilm capable of storing electric charges. As one example thereof,mention may be made of a silicon nitride film. Injection/discharge ofcharges into such charge storage regions causes each MISFET to beshifted in threshold value and to operate as a storage element. Theflash memories include a split gate type cell using a MONOS(Metal-Oxide-Nitride-Oxide-Semiconductor) film. Such a memory has thefollowing advantages: use of a silicon nitride film as a charge storageregion leads to an excellent data holding reliability because electriccharges are stored discretely as compared with a conductive floatinggate, and the excellent data holding reliability can reduce the filmthickness of the oxide films over and under the silicon nitride film,which enables a lower voltage for write/erase operation; and otheradvantages.

Japanese Unexamined Patent Publication No. 2005-347679 (PTL 1) andJapanese Unexamined Patent Publication No. 2003-309193 (PTL 2) eachdescribe the following technology: in a MONOS type nonvolatile memory,over a selection gate electrode (control gate electrode), an insulationfilm is formed, and at the sidewall of a lamination film including theselection gate electrode (control gate electrode), and the insulationfilm formed thereover, a memory gate electrode (memory gate) is formed.

Japanese Unexamined Patent Publication No. 2007-251079 (PTL 3) disclosesa problem of preventing a short circuit between the control gateelectrode and the memory gate electrode of a MONOS type nonvolatilememory. As a solving means therefor, there is described the followingtechnology: over the control gate electrode and the memory gateelectrode of the MONOS type nonvolatile memory, silicide is formed, andthe surface of the silicide is oxidized, thereby to improve thereliability and the manufacturing yield of the semiconductor device.

CITED LITERATURE

Patent Literature

[PTL 1]

-   Japanese Unexamined Patent Publication No. 2005-347679

[PTL 2]

-   Japanese Unexamined Patent Publication No. 2003-309193

[PTL 3]

-   Japanese Unexamined Patent Publication No. 2007-251079

SUMMARY OF THE INVENTION

A study by the present inventors revealed the following.

A split gate type nonvolatile memory using a MONOS film has thefollowing structure: a control gate electrode and a memory gateelectrode are adjacent to each other; under the control gate electrode,a silicon oxide film as a gate insulation film exists; under the memorygate electrode, a lamination gate insulation film having a chargestorage part exists; and the lamination gate insulation film alsoextends between the memory gate electrode and the control gate electrodeadjacent thereto. Therefore, the control gate electrode and the memorygate electrode are insulated and isolated from each other via thelamination gate insulation film. As the lamination gate insulation film,for example, an ONO (Oxide-Nitride-Oxide) film is formed as a laminationstructure of silicon oxide films and a silicon nitride film. Below, thelamination gate insulation film will be described as an ONO film.

However, the control gate electrode and the memory gate electrode areadjacent to each other via a thin ONO film. This structure causes a fearof a short-circuit failure or a leakage current between the control gateelectrode and the memory gate electrode. The short-circuit failurebetween the control gate electrode and the memory gate electrode reducesthe manufacturing yield of a semiconductor device having a nonvolatilememory. Whereas, the leakage current between the control gate electrodeand the memory gate electrode reduces the performances of asemiconductor device having a nonvolatile memory.

It is an object of the present invention to provide a technology capableof improving the performances of a semiconductor device.

Further, it is another object of the present invention to provide atechnology capable of improving the manufacturing yield of asemiconductor device.

The foregoing and other objects and novel features of the presentinvention will be apparent from the description of this specificationand the accompanying drawings.

Summaries of the representative ones of the inventions disclosed in thepresent application will be described in brief as follows.

A semiconductor device in accordance with a representative embodimentincludes: a semiconductor substrate; a lamination pattern formed overthe top of the semiconductor substrate; a second gate electrode formedover the top of the semiconductor substrate, and adjacent to thelamination pattern; a first gate insulation film formed between thefirst gate electrode and the semiconductor substrate; and a thirdinsulation film formed between the second gate electrode and thesemiconductor substrate, and between the lamination pattern and thesecond gate electrode. The lamination pattern has the first gateelectrode, a first insulation film over the first gate electrode, and asecond insulation film over the first insulation film. Further, thethird insulation film has a charge storage part in the inside thereof.Then, at the sidewall on the side of the lamination pattern adjacent tothe second gate electrode, the first insulation film is retreated fromthe first gate electrode and the second insulation film, and the upperend corner portion of the first gate electrode is rounded.

Further, a method for manufacturing a semiconductor device in accordancewith a representative embodiment is a method for manufacturing asemiconductor device, the semiconductor device, including: asemiconductor substrate; a first gate electrode and a second gateelectrode formed over the top of the semiconductor substrate, andadjacent to each other; a first gate insulation film formed between thefirst gate electrode and the semiconductor substrate; and a second gateinsulation film formed between the second gate electrode and thesemiconductor substrate, and having a charge storage part in the insidethereof. Then, the method includes the steps of: (a) preparing thesemiconductor substrate; (b) forming an insulation film for the firstgate insulation film over the main surface of the semiconductorsubstrate; (c) forming a first conductor film for the first gateelectrode over the insulation film; (d) forming a first insulation filmover the first conductor film; and (e) forming a second insulation filmover the first insulation film. The method further includes the stepsof: (f) patterning the second insulation film, the first insulationfilm, and the first conductor film, and forming a lamination patternhaving the first conductor film forming the first gate electrode, thefirst insulation film over the first conductor film, and the secondinsulation film over the first insulation film; and (g) side etching thefirst insulation film at a sidewall of the lamination pattern, andretreating the first insulation film from the first conductor film andthe second insulation film. Then, the method still further includes thesteps of: (h) after the step (g), forming a third insulation film forthe second gate insulation film, and having a charge storage part in theinside thereof over the main surface of the semiconductor substrate andthe sidewall of the lamination pattern; and (i) forming the second gateelectrode adjacent to the lamination pattern via the third insulationfilm over the third insulation film.

Effects obtainable by the representative ones of the inventionsdisclosed in the present application will be described in brief asfollows.

In accordance with representative embodiments, it is possible to improvethe performances of the semiconductor device.

Further, it is possible to improve the manufacturing yield of thesemiconductor device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an essential part cross-sectional view of a semiconductordevice which is one embodiment of the present invention;

FIG. 2 is a partially enlarged cross-sectional view of a portion of FIG.1 on an enlarged scale;

FIG. 3 is an equivalent circuit diagram of a memory cell;

FIG. 4 is a table showing one example of the conditions for applicationof voltages to respective sites of a selection memory cell for “write”,“erase”, and “read”;

FIG. 5 is a process flowchart showing a part of manufacturing steps of asemiconductor device which is one embodiment of the present invention;

FIG. 6 is an essential part cross-sectional view during a manufacturingstep of the semiconductor device of one embodiment of the presentinvention;

FIG. 7 is an essential part cross-sectional view of the semiconductordevice during a manufacturing step following that of FIG. 6;

FIG. 8 is an essential part cross-sectional view of the semiconductordevice during a manufacturing step following that of FIG. 7;

FIG. 9 is an essential part cross-sectional view of the semiconductordevice during a manufacturing step following that of FIG. 8;

FIG. 10 is an essential part cross-sectional view of the semiconductordevice during a manufacturing step following that of FIG. 9;

FIG. 11 is an essential part cross-sectional view of the semiconductordevice during a manufacturing step following that of FIG. 10;

FIG. 12 is an essential part cross-sectional view of the samesemiconductor device during a manufacturing step as that of FIG. 9;

FIG. 13 is an essential part cross-sectional view of the samesemiconductor device during a manufacturing step as that of FIG. 11;

FIG. 14 is an essential part cross-sectional view of the semiconductordevice during a manufacturing step following that of FIG. 11;

FIG. 15 is an essential part cross-sectional view of the semiconductordevice during a manufacturing step following that of FIG. 13;

FIG. 16 is an essential part cross-sectional view of the semiconductordevice during a manufacturing step following that of FIG. 15;

FIG. 17 is an essential part cross-sectional view of the semiconductordevice during a manufacturing step following that of FIG. 14;

FIG. 18 is an essential part cross-sectional view of the semiconductordevice during a manufacturing step following that of FIG. 17;

FIG. 19 is an essential part cross-sectional view of the semiconductordevice during a manufacturing step following that of FIG. 18;

FIG. 20 is an essential part cross-sectional view of the semiconductordevice during a manufacturing step following that of FIG. 19;

FIG. 21 is an essential part cross-sectional view of the samesemiconductor device during a manufacturing step as that of FIG. 20;

FIG. 22 is an essential part cross-sectional view of the semiconductordevice during a manufacturing step following that of FIG. 20;

FIG. 23 is an essential part cross-sectional view of the semiconductordevice during a manufacturing step following that of FIG. 22;

FIG. 24 is an essential part cross-sectional view of the semiconductordevice during a manufacturing step following that of FIG. 23;

FIG. 25 is an essential part cross-sectional view of the semiconductordevice during a manufacturing step following that of FIG. 24;

FIG. 26 is an essential part cross-sectional view of the semiconductordevice during a manufacturing step following that of FIG. 25;

FIG. 27 is an essential part cross-sectional view of the semiconductordevice during a manufacturing step following that of FIG. 26;

FIG. 28 is an essential part cross-sectional view of the semiconductordevice during a manufacturing step following that of FIG. 27;

FIG. 29 is an essential part cross-sectional view of a semiconductordevice of First Comparative Example;

FIG. 30 is an essential part cross-sectional view of a semiconductordevice of Second Comparative Example;

FIG. 31 is a graph showing the leakage current between the memory gateelectrode and the control gate electrode of a nonvolatile memory;

FIG. 32 is an essential part cross-sectional view of a semiconductordevice which is one embodiment of the present invention during amanufacturing step;

FIG. 33 is an essential part cross-sectional view of the semiconductordevice immediately before undergoing a cleaning treatment of Step S10during a manufacturing step;

FIG. 34 is an essential part cross-sectional view of the samesemiconductor device during a manufacturing step as that of FIG. 32;

FIG. 35 is an essential part cross-sectional view of the semiconductordevice during a manufacturing step following that of FIG. 32;

FIG. 36 is an essential part cross-sectional view of the samesemiconductor device during a manufacturing step as that of FIG. 35;

FIG. 37 is an essential part cross-sectional view of the semiconductordevice during a manufacturing step following that of FIG. 35;

FIG. 38 is an essential part cross-sectional view of the samesemiconductor device during a manufacturing step as that of FIG. 37;

FIG. 39 is an essential part cross-sectional view of the semiconductordevice during a manufacturing step following that of FIG. 37; and

FIG. 40 is an essential part cross-sectional view of the samesemiconductor device during a manufacturing step as that of FIG. 39.

PREFERRED EMBODIMENTS OF THE INVENTION

In description of the following embodiment, the embodiment may bedescribed in a plurality of divided sections or embodiments forconvenience, if required. However, unless otherwise specified, these arenot independent of each other, but are in a relation such that one is amodification example, or details, complementary explanation, or the likeof a part or the whole of the other. Further, in the followingembodiments, when a reference is made to the number of elements, and thelike (including number, numerical value, quantity, range, or the like),the number of elements is not limited to the specific number, but may begreater than or less than the specific number, unless otherwisespecified, and except the case where the number is apparently limited tothe specific number in principle, and other cases. Further in thefollowing embodiments, it is needless to say that the constitutionalelements (including element steps, or the like) are not alwaysessential, unless otherwise specified, and except the case where theyare apparently considered essential in principle, and other cases.Similarly, in the following embodiments, when a reference is made to theshapes, positional relationships, or the like of the constitutionalelements, or the like, it is understood that they include onessubstantially analogous or similar to the shapes or the like, unlessotherwise specified, unless otherwise considered apparently inprinciple, and except for other cases. This also applies to theforegoing numerical values and ranges.

Below, embodiments of the present invention will be described in detailsby reference to the accompanying drawings. Incidentally, in all thedrawings for describing the embodiments, the members having the samefunction are given the same reference signs and numerals, and a repeateddescription thereon is omitted. Further, in the following embodiments, adescription on the same or similar parts will not be repeated inprinciple, unless particularly required.

Further, in drawings to be used in embodiments, hatching may be omittedfor ease of understanding of the drawings even in a cross-sectionalview. Whereas, for ease of understanding of the drawings, hatching maybe provided even in a plan view

Embodiment 1

The present invention is a semiconductor device including a nonvolatilememory (nonvolatile storage element, flash memory, or nonvolatilesemiconductor storage device). The nonvolatile memory mainly uses atrapping insulation film (charge storable insulation film) as a chargestorage part. In the following embodiments, a nonvolatile memory will bedescribed with reference to a memory cell based on an n channel typeMISFET (MISFET: Metal Insulator Semiconductor Field Effect Transistor),and using a trapping insulation film. Further, the polarities (thepolarity of applied voltage and the polarity of carriers forwrite/erase/read) in the following embodiments are for describing theoperation in the case of a memory cell based on an n channel typeMISFET. When a memory cell is based on a p channel type MISFET, byreversing all the polarities of applied voltages, the conductivity typeof carriers, and the like, it is possible to obtain the same operationin principle.

A semiconductor device of the present embodiment and a manufacturingmethod thereof will be described by reference to the accompanyingdrawings.

FIG. 1 is an essential part cross-sectional view of the semiconductordevice of the present embodiment. The semiconductor device of thepresent embodiment is a semiconductor device including a nonvolatilememory. FIG. 1 shows an essential part cross-sectional view of a memorycell region of the nonvolatile memory. FIG. 2 is a partially enlargedcross-sectional view (essential part cross-sectional view) of a memorycell MC in the semiconductor device of the present embodiment, and showsa part of FIG. 1 on an enlarged scale. FIG. 3 is the equivalent circuitdiagram of the memory cell MC. Incidentally, FIG. 2 shows only alamination pattern 7, a memory gate electrode MG, and insulation films 3and 9, and a substrate region (a part of a semiconductor substrate 1forming a p type well PW1) immediately under them of the structure ofFIG. 1 for facilitating understanding thereof.

The nonvolatile memory shown in FIGS. 1 to 3 is a split gate type memorycell using a MONOS film.

As shown in FIGS. 1 and 2, in the semiconductor substrate (semiconductorwafer) 1 including a p type single-crystal silicon having a specificresistance of, for example, about 1 to 10 Ωcm, there is formed anelement isolation region for isolating elements (which corresponds to anelement isolation region 2 described later, but is herein not shown). Inan active region isolated (defined) by the element isolation region, thep type well PW1 is formed. In the p type well PW1 in the memory cellregion, there is formed the memory cell MC of a nonvolatile memoryincluding a memory transistor and a control transistor (selectiontransistor) as shown in FIGS. 1 and 2. In each memory cell region, aplurality of memory cells MC are formed in an array. Each memory cellregion is electrically isolated from other regions by the elementisolation regions.

As shown in FIGS. 1 to 3, the memory cell MC of the nonvolatile memoryin the semiconductor device of the present embodiment is a split gatetype memory cell using a MONOS film, and includes two MISFETs of acontrol transistor (selection transistor) having a control gateelectrode (selection gate electrode) CG, and a memory transistor havinga memory gate electrode (gate electrode for memory) MG, coupled to eachother.

Herein, a MISFET (Metal Insulator Semiconductor Field Effect Transistor)including a gate insulation film having a charge storage part, and amemory gate electrode MG is referred to as a memory transistor(transistor for storage). Whereas, a MISFET including a gate insulationfilm and a control gate electrode CG is referred to as a controltransistor (selection transistor or transistor for memory cellselection). Therefore, the memory gate electrode MG is the gateelectrode of the memory transistor. The control gate electrode CG is thegate electrode of the control transistor. The control gate electrode CGand the memory gate electrode MG are gate electrodes forming (the memorycell of) the nonvolatile memory.

Below, the configuration of the memory cell MC will be specificallydescribed.

As shown in FIGS. 1 and 2, the memory cell MC of the nonvolatile memoryhas n type semiconductor regions MS and MD for source and drain,respectively, formed in the p type well PW1 of the semiconductorsubstrate 1, the lamination pattern 7 formed over the top of thesemiconductor substrate 1 (p type well PW1), and a memory gate electrodeMG formed over the top of the semiconductor substrate 1 (p type wellPW1), and adjacent to the lamination pattern 7. The lamination pattern 7has the control gate electrode CG, an insulation film 5 over the controlgate electrode CG, and an insulation film 6 over the insulation film 5.Then, the memory cell MC of the nonvolatile memory further has aninsulation film (gate insulation film) 3 formed between the control gateelectrode CG and the semiconductor substrate 1 (p type well PW1), and aninsulation film 9 formed between the memory gate electrode MG and thesemiconductor substrate 1 (p type well PW1) and between the memory gateelectrode MG and the lamination pattern 7 (control gate electrode CG).

The lamination pattern 7 and the memory gate electrode MG extend and aredisposed side by side along the main surface of the semiconductorsubstrate 1 with the insulation film 9 interposed between the opposingside surfaces (sidewalls) thereof. The control gate electrode CG and thememory gate electrode MG are formed over the top of the semiconductorsubstrate 1 (p type well PW1), and over between the semiconductor regionMD and the semiconductor region MS via the insulation films 3 and 9(wherein, for the control gate electrode CG, via the insulation film 3,and for the memory gate electrode MG, via the insulation film 9). On theside of the semiconductor region MS, the memory gate electrode MG issituated. On the side of the semiconductor region MD, the control gateelectrode CG is situated.

The lamination pattern 7 including the control gate electrode CG and thememory gate electrode MG are adjacent to each other with the insulationfilm 9 interposed therebetween. The memory gate electrode MG is formedin a sidewall spacer form over the sidewall (side surface) 7 a of thelamination pattern 7 via the insulation film 9. This results in that thecontrol gate electrode CG and the memory gate electrode MG are adjacentto each other with the insulation film 9 interposed therebetween.Further, the insulation film 9 extends across both regions of a regionbetween the memory gate electrode MG and the semiconductor substrate 1(p type well PW1) and a region between the memory gate electrode MG andthe lamination pattern 7 (control gate electrode CG).

A portion of the insulation film 3 formed between the control gateelectrode CG and the semiconductor substrate 1 (p type well PW1) (i.e.,a portion of the insulation film 3 under the control gate electrode CG)functions as the gate insulation film of the control transistor.Whereas, a portion of the insulation film 9 between the memory gateelectrode MG and the semiconductor substrate 1 (p type well PW1) (i.e.,a portion of the insulation film 9 under the memory gate electrode MG)functions as the gate insulation film of the memory transistor (the gateinsulation film having a charge storage part in the inside thereof).

The insulation film 9 is a gate insulation film (ONO film) of alamination structure in which as an insulation film for storing electriccharges (i.e., a charge storage part), for example, a silicon nitridefilm 9 b, and as insulation films situated thereover and thereunder, forexample, a silicon oxide film 9 c and a silicon oxide film 9 a arestacked. Namely, the insulation film 9 includes a lamination film havingthe silicon oxide film (oxide film) 9 a, the silicon nitride film(nitride film) 9 b over the silicon oxide film 9 a, and the siliconoxide film (oxide film) 9 c over the silicon nitride film 9 b. In otherwords, the ONO (oxide-nitride-oxide) film in which the silicon oxidefilm 9 a, the silicon nitride film 9 b, and the silicon oxide film 9 care stacked sequentially from the side more distant from the memory gateelectrode MG forms the insulation film 9. The silicon nitride film 9 bis a trapping insulation film formed in the insulation film 9, andfunctions as a charge storage film for storing charges (charge storagepart). For this reason, the insulation film 9 can be regarded as aninsulation film having the charge storage part (herein, the siliconnitride film 9 b) in the inside thereof.

The semiconductor region MS is a semiconductor region functioning as oneof the source region or the drain region. The semiconductor region MD isa semiconductor region functioning as the other of the source region orthe drain region. Herein, the semiconductor region MS is a semiconductorregion functioning as the source region. The semiconductor region MD isa semiconductor region functioning as the drain region. Thesemiconductor regions MS and MD each include a semiconductor regionincluding n type impurities introduced therein (n type impuritydiffusion layer), and each have a LDD (lightly doped drain) structure.Namely, the semiconductor region MS for source has an n⁺ typesemiconductor region 11 a, and an n⁺ type semiconductor region 12 ahaving a higher impurity concentration than that of the n⁻ typesemiconductor region 11 a. The semiconductor region MD for drain has ann⁻ type semiconductor region 11 b, and an n⁺ type semiconductor region12 b having a higher impurity concentration than that of the n⁻ typesemiconductor region 11 b. The n⁺ type semiconductor region 12 a isdeeper in junction depth, and higher in impurity concentration than then⁻ type semiconductor region 11 a. Whereas, the n⁺ type semiconductorregion 12 b is deeper in junction depth, and higher in impurityconcentration than the n⁻ type semiconductor region 11 b.

Over the sidewalls of the memory gate electrode MG and the control gateelectrode CG (the sidewalls on the sides not adjacent to each other),sidewall insulation films (sidewalls or sidewall spacers) SW includingan insulator such as silicon oxide (silicon oxide film or insulationfilm) are formed. Namely, over the sidewall (side surface) on the sideof the memory gate electrode MG opposite to the side thereof adjacent tothe control gate electrode CG via the insulation film 9, and over thesidewall (side surface) on the side of the control gate electrode CGopposite to the side thereof adjacent to the memory gate electrode MGvia the insulation film 9, the sidewall insulation films SW are formed.

The n⁻ type semiconductor region 11 a of the source part is formed inself-alignment with the sidewall of the memory gate electrode MG. The n⁺type semiconductor region 12 a is formed in self-alignment with the sidesurface of the sidewall insulation film SW over the sidewall of thememory gate electrode MG (the side surface on the side opposite to theside in contact with the memory gate electrode MG). Accordingly, thelow-concentration n⁻ type semiconductor region 11 a is formed under thesidewall insulation film SW over the sidewall of the memory gateelectrode MG. The high-concentration n⁺ type semiconductor region 12 ais formed outside the low-concentration n⁻ type semiconductor region 11a. Therefore, the low-concentration n⁻ type semiconductor region 11 a isformed in such a manner as to be adjacent to the channel region of thememory transistor. The high-concentration n⁺ type semiconductor region12 a is formed in such a manner as to be in contact with thelow-concentration n⁻ type semiconductor region 11 a, and to be spacedapart from the channel region of the memory transistor by the thicknessof the n⁻ type semiconductor region 11 a.

The n⁻ type semiconductor region 11 b of the drain part is formed inself-alignment with the sidewall of the control gate electrode CG. Then⁺ type semiconductor region 12 b is formed in self-alignment with theside surface of the sidewall insulation film SW over the sidewall of thecontrol gate electrode CG (the side surface on the side opposite to theside in contact with the control gate electrode CG). Accordingly, thelow-concentration n⁻ type semiconductor region lib is formed under thesidewall insulation film SW over the sidewall of the control gateelectrode CG. The high-concentration n⁺ type semiconductor region 12 bis formed outside the low-concentration n⁻ type semiconductor region 11b. Therefore, the low-concentration n⁻ type semiconductor region 11 b isformed in such a manner as to be adjacent to the channel region of thecontrol transistor. The high-concentration n⁺ type semiconductor region12 b is formed in such a manner as to be in contact with thelow-concentration n⁻ type semiconductor region 11 b, and to be spacedapart from the channel region of the control transistor by the thicknessof the n⁻ type semiconductor region 11 b.

Under the insulation film 9 of the memory gate electrode MG, the channelregion of the memory transistor is formed. Under the insulation film 3under the control gate electrode CG, the channel region of the controltransistor is formed. In a channel formation region of the controltransistor under the insulation film 3 under the control gate electrodeCG, a semiconductor region (p type semiconductor region or n typesemiconductor region) for adjustment of the threshold value of thecontrol transistor is formed, if required. In a channel formation regionof the memory transistor under the insulation film 9 under the memorygate electrode MG, a semiconductor region (p type semiconductor regionor n type semiconductor region) for adjustment of the threshold value ofthe memory transistor is formed, if required.

The control gate electrode CG includes a conductor (conductor film), andpreferably includes an n type silicon film 4 n such as an n typepolysilicon (impurities-doped polysilicon or doped polysilicon).Specifically, the control gate electrode CG includes a patterned n typesilicon film 4 n.

The control gate electrode CG has one of features as follows: theinsulation film 5 and the insulation film 6 are stacked thereover,thereby to form the lamination pattern 7. The lamination pattern 7 isformed in the following manner: as described later, over the mainsurface of the semiconductor substrate 1, the n type silicon film 4 n,the insulation film 5, and the insulation film 6 are formed sequentiallyfrom the bottom, resulting in a lamination film; and the lamination filmis patterned. Therefore, the lamination pattern 7 includes the patternedn type silicon film 4 n, insulation film 5, and insulation film 6. Then,as one of other features, at the sidewall (side surface) 7 a on the sideof the lamination pattern 7 adjacent to the memory gate electrode MG,the insulation film 5 is retreated (is recessed) from the control gateelectrode CG and the insulation film 6.

Further, in the present embodiment, derived from the manufacturingprocess, also at the sidewall (side surface) 7 b on the side of thelamination pattern 7 opposite to the side thereof adjacent to the memorygate electrode MG, the insulation film 5 is retreated from the controlgate electrode CG and the insulation film 6. However, the importantpoint is that at the sidewall 7 a on the side of the lamination pattern7 adjacent to the memory gate electrode MG, the insulation film 5 isretreated from the control gate electrode CG and the insulation film 6.

At the sidewalls 7 a and 7 b of the lamination pattern 7, the insulationfilm 5 is retreated from the control gate electrode CG and theinsulation film 6. This is due to the following: as described later, alamination film of the n type silicon film 4 n, the insulation film 5,and the insulation film 6 formed over the main surface of thesemiconductor substrate 1 is patterned, thereby to form the laminationpattern 7; then, at the sidewalls 7 a and 7 b of the lamination pattern7, the insulation film 5 is side etched to be retreated from the controlgate electrode CG (n type silicon film 4 n) and the insulation film 6.For this reason, as the materials for the insulation film 5, it isnecessary to select such materials as to be capable of enhancing theetching selectivity of the insulation film 5 relative to those of the ntype silicon film 4 n and the insulation film 6 (i.e., capable ofenhancing the etching rate of the insulation film 5 relative to theetching rates of the n type silicon film 4 n and the insulation film 6).From this viewpoint, the insulation film 5 and the insulation film 6 arerequired to include mutually different materials (insulation materials).In the case of the present embodiment 1, it is preferable that theinsulation film 5 is a silicon oxide film, and that the insulation film6 is a silicon nitride film. This is for the following reason. Foretching of a silicon oxide film and a silicon film, and etching of asilicon oxide film and a silicon nitride film, it is possible to enhancethe selectivity of the silicon oxide film. However, for etching of asilicon film and a silicon nitride film, it is difficult to ensure ahigh selectivity. For this reason, in the present embodiment, thesilicon oxide film which can be enhanced in selectivity relative to therespective silicon film and silicon nitride film is formed as theinsulation film 5 between the n type silicon film 4 n and the insulationfilm 6. This results in that the insulation film 5 is retreated from then type silicon film 4 n and insulation film 6, which allows formation ofthe structure as in the present embodiment.

At the sidewalls 7 a and 7 b of the lamination pattern 7, the insulationfilm 5 is retreated from the control gate electrode CG and theinsulation film 6. As a result, in the lamination pattern 7, the planedimensions (plane area) of the insulation film 5 are (is) smaller thanthe plane dimensions (plane area) of the insulation film 6, and issmaller than the plane dimensions (plane area) of the control gateelectrode CG. The insulation film 5 has a plane configuration to betwo-dimensionally included in the insulation film 6, and to be alsotwo-dimensionally included in the control gate electrode CG. On theother hand, in the lamination pattern 7, the insulation film 6 hasalmost the same plane configuration (plane dimensions) as the planeconfiguration (plane dimensions) of the control gate electrode. CG.Herein, for the control gate electrode CG, the insulation film 5, andthe insulation film 6, plane dimensions and plane configurationcorrespond to the plane dimensions and plane configuration as seen inplan view parallel to the main surface of the semiconductor substrate 1,respectively.

In other words, the opposite sides of the insulation film 5 areretreated from the control gate electrode CG and the insulation film 6.Accordingly, the width of the insulation film 5 along the transversedirection of the cross section of the memory cell shown in FIG. 2 isshorter than those of the control gate electrode CG and the insulationfilm 6. Over the upper end of the control gate CG, and under the lowerend of the insulation film 6, there are regions in which the insulationfilm 5 is not formed.

Further, in the present embodiment, as one of still other features, atthe sidewall 7 a on the side of the lamination pattern 7 adjacent to thememory gate electrode MG, the upper end corner portion (corner portion)C1 of the control gate electrode CG is rounded (is roundish, or has around shape). In the present embodiment, derived from the manufacturingprocess, also at the sidewall 7 b on the side of the lamination pattern7 opposite to the side thereof adjacent to the memory gate electrode MG,the upper end corner portion (corner portion) C2 of the control gateelectrode CG is rounded (is roundish, or has a round shape). However,the important point is that at the sidewall 7 a on the side of thelamination pattern 7 adjacent to the memory gate electrode MG, the upperend corner portion C1 of the control gate electrode CG is rounded.

Herein, the upper end corner portion C1 of the control gate electrode CGcorresponds to the corner portion between the top surface of the controlgate electrode CG and the side surface on the side of the control gateelectrode CG adjacent to the memory gate electrode MG (the side surfacecorresponding to the sidewall 7 a). Whereas, the upper end cornerportion C2 of the control gate electrode CG corresponds to the cornerportion between the top surface of the control gate electrode CG and theside surface on the side of the control gate electrode CG opposite tothe side thereof adjacent to the memory gate electrode MG (the sidesurface corresponding to the sidewall 7 b).

Further, it is preferable that the thickness T2 of the insulation film 5forming the lamination pattern 7 is larger than the thickness T1 of theinsulation film 3 situated under the control gate electrode CG (i.e.,T2>T1). Whereas, the insulation film 3 can be formed of, for example, asilicon oxide film or a silicon oxynitride film. However, it is morepreferable that as the insulation film 3, a silicon oxynitride film isused. This is in order to minimize etching (side etching) of theinsulation film 3 situated under the control gate electrode CG when atthe sidewalls 7 a and 7 b of the lamination pattern 7, the insulationfilm 5 is side etched to form a structure in which the insulation film 5is retreated from (the n type silicon film 4 n forming) the control gateelectrode CG, and the insulation film 6. As a result, it is possible tomore improve the reliability of the insulation film 3 as the gateinsulation film.

Further, for the insulation film 3, other than the silicon oxide film,the silicon oxynitride film, or the like, there may be used a metaloxide film having a higher dielectric constant than that of the siliconnitride film, such as a hafnium oxide film, an aluminum oxide film(alumina), or a tantalum oxide film.

Further, as described later, at the sidewall of the lamination pattern7, the insulation film 5 is side etched to be retreated from the controlgate electrode CG and the insulation film 6. Then, the insulation film 9is formed. Accordingly, in a region in which the insulation film 5 isretreated at the sidewall 7 a of the lamination pattern 7 (the sidewall7 a on the side adjacent to the memory gate electrode MG) (the regioncorresponding to a region 30 a shown in FIG. 13 described later), aportion of the insulation film 9 penetrates. Specifically, theinsulation film 9 includes a lamination film of the silicon oxide film 9a, the silicon nitride film 9 b, and the silicon oxide film 9 c.Accordingly, in a region in which the insulation film 5 is retreated atthe sidewall 7 a of the lamination pattern 7 (the sidewall 7 a on theside adjacent to the memory gate electrode MG) (the region correspondingto the region 30 a shown in FIG. 13 described later), a portion of thesilicon nitride film 9 b also penetrates.

The memory gate electrode MG includes a conductor (conductor film).However, it preferably includes an n type silicon film 10 n such as an ntype polysilicon (impurities-doped polysilicon or doped polysilicon).The memory gate electrode MG is formed in the following manner. Asdescribed later, the n type silicon film 10 n formed in such a manner asto cover the lamination pattern 7 over the semiconductor substrate 1 isanisotropically etched. Thus, over the sidewall of the laminationpattern 7, the n type silicon film 10 n is left via the insulation film9. Accordingly, the memory gate electrode MG is formed in a sidewallspacer form over the sidewall of the lamination pattern 7 via theinsulation film 9.

Over the top (top surface) of (the n type silicon film 10 n forming) thememory gate electrode MG, and the top surfaces (surfaces of) the n⁺ typesemiconductor regions 12 a and 12 b, a metal silicide layer (metalsilicide film) 21 is formed by a salicide process or the like. The metalsilicide layer 21 includes, for example, a cobalt silicide layer or anickel silicide layer. The metal silicide layer 21 can lower thediffusion resistance and the contact resistance. The combination of then type silicon film 10 n forming the memory gate electrode MG, and themetal silicide layer 21 over the top thereof can also be regarded as thememory gate electrode MG.

On the other hand, over the control gate electrode CG, the insulationfilms 5 and 6 are stacked. Accordingly, over the top of the control gateelectrode CG, a metal silicide layer such as the metal silicide layer 21is not formed. Namely, over the control gate electrode CG, theinsulation film 5 is formed in contact with the control gate electrodeCG. Over the insulation film 5, the insulation film 6 is formed incontact with the insulation film 5.

Over the semiconductor substrate 1, an insulation film 22, and aninsulation film 23 over the insulation film 22 are formed in such amanner as to cover the lamination pattern 7, the memory gate electrodeMG, and the sidewall insulation film SW. The insulation film 22 isthinner than the insulation film 23, and preferably includes a siliconnitride film. The insulation film 23 is thicker than the insulation film22, and preferably includes a silicon oxide film. The insulation films 5and 6 formed over the control gate CG are interposed between the topsurface of the control gate electrode CG and the insulation film 22. Asdescribed later, in the insulation films 22 and 23, contact holes CNTare formed. In each contact hole CNT, a plug PG is embedded. Over theinsulation film 23 including the plug PG embedded therein, a wire M1,and the like are formed, but are not shown in FIGS. 1 and 2.Incidentally, the insulation film 23 can function as an interlayerinsulation film. The insulation film 22 can function as an etchingstopper film for forming contact holes CNT described later in theinsulation film 23.

FIG. 4 is a table showing one example of the conditions for applyingvoltages to respective sites of a selection memory cell at the times of“write”, “erase”, and “read” of the present embodiment. In the table ofFIG. 4, there are shown the voltage Vd to be applied to the drain region(semiconductor region MD) of the memory cell (selection memory cell) asshown in FIGS. 2 and 3, the voltage Vcg to be applied to the controlgate electrode CG, the voltage Vmg to be applied to the memory gateelectrode MG, the voltage Vs to be applied to the source region(semiconductor region MS), and the base voltage Vb to be applied to thep type well PW1 at respective times of “write”, “erase”, and “read”.Incidentally, the data shown in the table of FIG. 4 is one example ofthe conditions for application of voltages, is not exclusive, and ifrequired, may be variously changed. Further, in the present embodiment,injection of electrons into the silicon nitride film 9 b which is thecharge storage part in the insulation film 9 of the memory transistor isdefined as “write”, and injection of holes (positive holes) is definedas “erase”.

For the write method, hot electron write called so-called SSI (SourceSide Injection) method can be used. For example, the voltages as shownin the row of “write” of FIG. 4 are applied to respective sites of theselection memory cell for performing write. Thus, electrons are injectedinto the silicon nitride film 9 b in the insulation film 9 of theselection memory cell. Hot electrons occur in the channel region(between source and drain) under between two gate electrodes (the memorygate electrode MG and the control gate electrode CG). The hot electronsare injected into the silicon nitride film 9 b which is the chargestorage part in the insulation film 9 under the memory gate electrodeMG. The injected hot electrons (electrons) are trapped at the trap levelin the silicon nitride film 9 b in the insulation film 9. As a result,the threshold voltage of the memory transistor is increased.

For the erase method, a BTBT (Band-To-Band Tunneling) phenomenon hothole injection erase method can be used. Namely, holes (positive holes)generated by BTBT (Band-To-Band Tunneling) phenomenon are injected intothe charge storage part (the silicon nitride film 9 b in the insulationfilm 9), thereby to perform erase. For example, the voltages as shown inthe row of “erase” of FIG. 4 are applied to respective sites of theselection memory cell for performing erase. Thus, holes (positive holes)are generated by the BTBT (Band-To-Band Tunneling) phenomenon toaccelerate the electric field. Thus, holes are injected into the siliconnitride film 9 b in the insulation film 9 of the selection memory cell.As a result, the threshold voltage of the memory transistor is reduced.

For read, for example, the voltages as shown in the row of “read” ofFIG. 4 are applied to respective sites of the selection memory cell forperforming read. The voltage Vmg to be applied to the memory gateelectrode MG for read is set at a value between the threshold voltage ofthe memory transistor in the write state and the threshold voltagethereof in the erase state. This enables discrimination between thewrite state and the erase state.

Then, a description will be given to a method for manufacturing asemiconductor device of the present embodiment.

FIG. 5 is a process flowchart showing a part of manufacturing steps ofthe semiconductor device of the present embodiment. FIGS. 6 to 28 areeach an essential part cross-sectional view of the semiconductor deviceof the present embodiment during a manufacturing step. In respectivediagrams of FIGS. 6 to 11, FIG. 14, FIGS. 17 to 20, and FIGS. 22 to 28,there are shown essential part cross-sectional views of a memory cellregion (a region in which the memory cell MC of the nonvolatile memoryis formed) 1A and a peripheral circuit region (a region in which othercircuits than the nonvolatile memory are formed) 1B. There are shown themanner in which the memory cell MC is formed in the memory cell region1A, and the MISFET is formed in the peripheral circuit region 1B. It isalso acceptable that the memory cell region 1A is not adjacent to theperipheral circuit region 1B. However, for facilitating understandingthereof, in FIGS. 6 to 11, FIG. 14, FIGS. 17 to 20, and FIGS. 22 to 28,the peripheral circuit region 1B is shown adjacent to the memory cellregion 1A. Further, in FIGS. 6 to 11, FIG. 14, FIGS. 17 to 20, and FIGS.22 to 28, the memory cell region 1A and the peripheral circuit region 1Bare shown separate from each other. However, these are formed in thesame semiconductor substrate 1. Further, in FIGS. 12, 13, 15, 16, and21, there are shown the lamination pattern 7 formed in the memory cellregion 1A, and the neighboring regions. Herein, examples of theperipheral circuits include processor such as CPU, control circuit,sense amplifier, column decoder, row decoder, and input/output circuit.

Further, in the present embodiment, a description will be given to thecase where in the memory cell region 1A, n channel type MISFETs (thecontrol transistor and the memory transistor) are formed. However, thefollowing is also acceptable: the conductivity type is reversed to formp channel type MISFETs (the control transistors and the memorytransistors) in the memory cell region 1A. Similarly, in the presentembodiment, a description will be given to the case where in theperipheral circuit region 1B, n channel type MISFETs are formed.However, the following is also acceptable: the conductivity type isreversed to form p channel type MISFETs in the peripheral circuit region1B. Alternatively, in the peripheral circuit region 1B, CMISFETs(Complementary MISFETs), or the like can be formed.

As shown in FIG. 6, first, a semiconductor substrate (semiconductorwafer) 1 including p type single-crystal silicon having a specificresistance of, for example, about 1 to 10 Ωcm, or the like is prepared(provided) (Step S1 of FIG. 5). Then, in the main surface of thesemiconductor substrate 1, an element isolation region (elementisolation insulation region) 2 defining (bordering) the active region isformed (Step S2 of FIG. 5). The element isolation region 2 includes aninsulator such as silicon oxide, and can be formed by, for example, theSTI (Shallow Trench Isolation) method or the LOCOS (Local Oxidization ofSilicon) method. For example, in the main surface of the semiconductorsubstrate 1, grooves for element isolation are formed. Then, in thegrooves for element isolation, an insulation film including, forexample, silicon oxide is embedded. As a result, the element isolationregion 2 can be formed.

Then, in the memory cell region 1A of the semiconductor substrate 1, a ptype well PW1 is formed, and in the peripheral circuit region 1B, a ptype well PW2 is formed (Step S3 of FIG. 5). The p type wells PW1 andPW2 can be formed by ion-implanting p type impurities such as boron (B)into the semiconductor substrate 1, or by other methods. The p typewells PW1 and PW2 are formed from the main surface to a predetermineddepth of the semiconductor substrate 1.

Then, in order to adjust the threshold voltage of the control transistorto be formed later in the memory cell region 1A, if required, thesurface part (surface layer part) of the p type well PW1 of the memorycell region 1A is subjected to channel dope ion implantation. Whereas,in order to adjust the threshold voltage of the MISFET formed later inthe peripheral circuit region 1B, if required, the surface part (surfacelayer part) of the p type well PW2 of the peripheral circuit region 1Bis subjected to channel dope ion implantation.

Then, by dilute hydrofluoric acid cleaning or the like, the surface ofthe semiconductor substrate 1 (p type wells PW1 and PW2) is cleaned.Then, over the main surface of the semiconductor substrate 1 (thesurfaces of the p type wells PW1 and PW2), the insulation film 3 for thegate insulation film is formed (Step S4 of FIG. 5). The insulation film3 can be formed of, for example, a thin silicon oxide film or siliconoxynitride film. However, it is more preferable that, as the insulationfilm 3, a silicon oxynitride film is used. Use of a silicon oxynitridefilm as the insulation film 3 can more precisely prevent the following:when the insulation film 5 described later is side etched (in the caseof the present embodiment, corresponding to the cleaning step of StepS12 described later, in the case of Embodiment 2 described later,corresponding to the cleaning step of Step S10 a), the insulation film 3is etched (side etched). When a silicon oxynitride film is used as theinsulation film 3, the silicon oxynitride film can be formed bynitriding the silicon oxide film formed by an thermal oxidation method,or by other methods. The film thickness (formed film thickness) T1 ofthe insulation film 3 can be set at, for example, about 2 to 3 nm.

Then, over the entire main surface of the semiconductor substrate 1,namely, over the insulation film 3, a silicon film (first conductorfilm) 4 is formed (deposited) as a conductor film for gate electrode(Step S5 of FIG. 5). The silicon film 4 includes a polysilicon film, andcan be formed by using a CVD (Chemical Vapor Deposition) method, or thelike. The film thickness (deposited thickness) of the silicon film 4 canbe set at, for example, about 100 to 200 nm.

After formation of the silicon film 4, over the silicon film 4, aphotoresist pattern is formed by using a photolithography method(although not shown herein, the photoresist pattern is formed in theentire peripheral circuit region 1B). By using the photoresist patternas a mask, n type impurities are introduced into the (silicon film 4) ofthe memory cell region 1A by an ion implantation method or the like. Asa result, in the memory cell region 1A, the n type silicon film 4 n isformed. Namely, n type impurities are introduced into the silicon film 4in the memory cell region 1A. As a result, the silicon film 4 in thememory cell region 1A becomes an n type silicon film 4 n doped with ntype impurities.

Then, as shown in FIG. 7, over the n type silicon film 4 n in the memorycell region 1A, and over the silicon film 4 in the peripheral circuitregion 1B, the insulation film (first insulation film) 5 is formed (StepS6 of FIG. 5). The insulation film 5 preferably includes a silicon oxidefilm, and can be formed by oxidizing the top surfaces (upper layerparts) of the n type silicon film 4 n and the silicon film 4. Theinsulation film 5 can be formed by thermal oxidation. However, it isfurther preferable that the insulation film 5 is formed by ISSG (In SituSteam Generation) oxidation. The film thickness (formed film thickness)T2 of the insulation film 5 can be set at, for example, about 5 to 10nm.

Further, the thickness (formed film thickness) T2 of the insulation film5 formed in Step S6 is preferably larger than the thickness (formed filmthickness) T1 of the insulation film 3 formed in Step S4 (i.e., T2>T1).This can inhibit or prevent the insulation film 3 from being etched(side etched) when the insulation film 5 is side etched later (in thecase of the present embodiment, corresponding to the cleaning step ofStep S12 described later, in the case of Embodiment 2 described later,corresponding to the cleaning step of Step S10 a).

Then, over the insulation film 5, the insulation film (second insulationfilm) 6 is formed (Step S7 of FIG. 5). This results in a state in whichin the memory cell region 1A, over the main surface of the semiconductorsubstrate 1, namely, over the insulation film 3, a lamination film ofthe n type silicon film 4 n, the insulation film 5, and the insulationfilm 6 is formed. The insulation film 6 is an insulation film includinga different insulation material from that for the insulation film 5. Theinsulation film 6 preferably includes a silicon nitride film, and can beformed by a CVD method, or the like. The film thickness (formed filmthickness) T3 of the insulation film 6 can be set at, for example, about50 to 100 nm. Further, in the peripheral circuit region 1B, over themain surface of the semiconductor substrate 1, namely, over theinsulation film 3, a lamination film of the silicon film 4, theinsulation film 5, and the insulation film 6 is formed.

The insulation film 6 is provided in order to prevent the formation of ametal silicide layer by a salicide process over the control gateelectrode CG to be formed later. The insulation film 5 is provided inorder to round the upper end corner portion C1 of the control gateelectrode CG to be formed later. The insulation film 5 has theinsulation film 6 over the top thereof, and hence keeps the thickness(formed film thickness) T2 upon formation of the insulation film 5 atStep S6 even in a semiconductor device after manufacturing. On the otherhand, the insulation film 6 may be etched in the direction of thicknessin various steps after deposition. Therefore, the thickness of theinsulation film 6 in the semiconductor device after manufacturing isdecreased from the thickness (formed film thickness) T3 upon formationof the insulation film 6 at Step S7, resulting in a smaller value thanthe thickness T3.

The thickness (formed film thickness) T3 of the insulation film 6 formedat Step S7 is preferably larger than the thickness (formed filmthickness) T2 of the insulation film 5 formed at Step S6 (i.e., T3>T2).This facilitates ensuring of the thickness of the insulation film 6 upto a metal silicide layer 21 formation step (salicide process) describedlater. This prevents a metal film 20 described later from being incontact with the control gate electrode CG, which facilitates preventionof the formation of the metal silicide layer 21 over the control gateelectrode CG. Further, it is further preferable that, in a semiconductordevice after manufacturing, the thickness of the insulation film 6 islarger than the thickness of the insulation film 5. As a result, even ifthere occur fluctuations in amount of loss when the film thickness ofthe insulation film 6 is decreased in various steps after deposition ofthe insulation film 6, it becomes possible to prevent the formation ofthe metal silicide layer 21 over the control gate electrode CG withreliability.

Then, the lamination film of the n type silicon film 4 n, the insulationfilm 5, and the insulation film 6 in the memory cell region 1A ispatterned by etching (Step S8 of FIG. 5). The patterning step of Step S8can be carried out, for example, in the following manner.

Namely, over the insulation film 6, using a photolithography method, aphotoresist pattern (although not shown herein, the photoresist patternis formed in a control gate electrode CG forming region and the entireperipheral circuit region 1B) is formed. Using the photoresist patternas an etching mask, the insulation film 6, the insulation film 5, andthe n type silicon film 4 n are etched (dry etched) to be patterned.Then, the photoresist pattern is removed.

As another form, over the insulation film 6, using a photolithographymethod, a photoresist pattern (although not shown herein, thephotoresist pattern is formed in the control gate electrode CG formingregion and the entire peripheral circuit region 1B) is formed. Using thephotoresist pattern as an etching mask, the insulation film 6 is etched,and patterned. Then, the photoresist pattern is removed. Then, using thepatterned insulation film 6 as an etching mask, portions of theunderlying insulation film 5 and n type silicon film 4 n exposedtherefrom are etched, thereby to pattern the insulation film 5 and the ntype silicon film 4 n.

Thus, at Step S8, the lamination film of the n type silicon film 4 n,the insulation film 5, and the insulation film 6 is patterned. As shownin FIG. 8, in the memory cell region 1A, the lamination pattern(patterned lamination film) 7 is formed. The lamination pattern 7includes the lamination film of the n type silicon film 4 n, theinsulation film 5, and the insulation film 6 sequentially formed fromthe bottom. At this step, in the peripheral circuit region 1B, asdescribed above, the photoresist pattern has been formed, and hencepatterning is not performed.

The n type silicon film 4 n (i.e., patterned n type silicon film 4 n)forming the lamination pattern 7 formed in the memory cell region 1Abecomes the control gate electrode CG of the control transistor. Theremaining portion of the insulation film 3 under the control gateelectrode CG becomes the gate insulation film of the control transistor.This results in the following state: the lamination pattern 7 has the ntype silicon film 4 n forming the control gate electrode CG, theinsulation film 5 over the n type silicon film 4 n, and the insulationfilm 6 over the insulation film 5, and is formed over the semiconductorsubstrate 1 (p type well PW1) via the insulation film 3 as the gateinsulation film.

In the memory cell region 1A, portions of the insulation film 3 otherthan the portion thereof covered with the control gate electrode CG(lamination pattern 7) (i.e., portions of the insulation film 3 otherthan the portion thereof serving as the gate insulation film) may beremoved by dry etching performed at the patterning step of Step S8, orperforming wet etching after the dry etching. In the memory cell region1A, portions of the insulation film 3 other than the portion thereofcovered with the control gate electrode CG (i.e., portions of theinsulation film 3 other than the portion thereof serving as the gateinsulation film) are preferably removed at this stage. However, evenwhen the portions remain at this stage, they are removed by the cleaningstep of Step S12 described later.

The sidewall (side surface) of the lamination pattern 7 at this stage isalmost flat, and is preferably almost perpendicular to the main surfaceof the semiconductor substrate 1. For this reason, in the memory cellregion 1A, the plane configurations (plane dimensions) of the n typesilicon film 4 n, the insulation film 5, and the insulation film 6forming the lamination pattern 7 are mutually almost the same.Accordingly, in the lamination pattern 7, over the control gateelectrode CG, the insulation film 5 and the insulation film 6 havingalmost the same plane configuration (plane dimensions) as that (those)of the control gate electrode CG are stacked.

Then, using a photolithography method, such a photoresist pattern (notshown) as to cover the lamination pattern 7 in the memory cell region1A, and as to expose the entire peripheral circuit region 1B is formed.Then, using the photoresist pattern as an etching mask, as shown in FIG.9, the insulation film 6 formed in the peripheral circuit region 1B isetched, and removed (Step S9 of FIG. 5). At this step, in the peripheralcircuit region 1B, the insulation film 5 functions as an etching stopperfilm. Further, in Step S9, the lamination pattern 7 in the memory cellregion 1A is covered with the photoresist pattern. Accordingly, theinsulation film 6 of the lamination pattern 7 in the memory cell region1A is left without being etched. Then, the photoresist pattern isremoved.

As a result, as shown in FIG. 9, the lamination pattern 7 in the memorycell region 1A is still in a lamination structure of the control gateelectrode CG (n type silicon film 4 n), the insulation film 5, and theinsulation film 6. However, in the peripheral circuit region 1B, theinsulation film 6 has ceased to remain.

Then, a cleaning treatment is carried out to purify the main surface ofthe semiconductor substrate 1 (Step S10 of FIG. 5).

In the present embodiment, the cleaning treatment of Step S10 is carriedout without using hydrofluoric acid (HF). As the cleaning treatment ofStep S10, one or both of cleaning with an APM (Ammonia-Hydrogen PeroxideMixture) solution (i.e., a solution mixture of ammonia, hydrogenperoxide, and water), and cleaning with a HPM (Hydrochloricacid-Hydrogen Peroxide Mixture) solution (i.e., a solution mixture ofhydrochloric acid, hydrogen peroxide, and water) are preferablyperformed. At the cleaning treatment of Step S10, a cleaning solutionnot containing hydrofluoric acid is used. For this reason, etching ofthe silicon oxide film is inhibited or prevented. The insulation film 5preferably includes silicon oxide. Therefore, even when the cleaningtreatment of Step S10 is performed, in the lamination pattern 7 in thememory cell region 1A, side etching of the insulation film 5 is notcaused. Whereas, in the peripheral circuit region 1B, the insulationfilm 5 is left.

Then, sacrifice oxidation is performed (Step S11 of FIG. 5). Thesacrifice oxidation of Step S11 can be performed by subjecting thesemiconductor substrate 1 to an oxidation treatment, and can bepreferably performed by thermal oxidation. However, the sacrificeoxidation is further preferably performed by ISSG oxidation.

The purpose of performing the sacrifice oxidation of Step S11 is asfollows: in the step of patterning the lamination film of the n typesilicon film 4 n, the insulation film 5, and the insulation film 6 inthe memory cell region 1A by etching (corresponding to the Step S8), thesemiconductor substrate 1 is damaged by etching; for this reason, thisportion is oxidized, thereby to eliminate the damage. Further, it isalso possible to eliminate collectively the damage of the side surfaceof the control gate electrode CG exposed by etching. Further, althoughnot shown, before a step of a cleaning treatment described later(corresponding to Step S12 described later), there is an ionimplantation step in which a semiconductor region for adjustment of thethreshold value of the memory transistor is formed. The sacrifice oxidefilm (silicon oxide film) 8 formed by sacrifice oxidation also plays arole of preventing the damage in the ion implantation step.

By the sacrifice oxidation of Step S11, as shown in FIG. 10, in thememory cell region 1A, portions of the main surface (surface) of thesemiconductor substrate 1 (p type well PW1) not covered with thelamination pattern 7 (control gate electrode CG), and the side surfaces(sidewalls) of the n type silicon film 4 n (control gate electrode CG)of the lamination pattern 7 are oxidized. As a result, a sacrifice oxidefilm (silicon oxide film) 8 is formed. Whereas, in the peripheralcircuit region 1B, the surface of the insulation film 5 is oxidized. Asa result, the sacrifice oxide film (silicon oxide film) 8 is formed. Thefilm thickness of the sacrifice oxide film 8 can be set at, for example,about 3 to 6 nm. When the sacrifice oxidation of Step S11 is performedwith ISSG oxidation, not only the Si region (herein, the semiconductorsubstrate 1 and the n type silicon film 4 n in the memory cell region1A) but also the SiN region (herein, the insulation film 6) can beoxidized. Therefore, the top surface and the side surfaces (sidewalls)of the insulation film 6 (silicon nitride film) of the laminationpattern 7 in the memory cell region 1A are also oxidized. As a result,the sacrifice oxide film 8 is formed.

By performing the sacrifice oxidation of Step S11, in the memory cellregion 1A, the gate insulation film after gate processing (correspondingto the patterning step of the Step S8) (corresponding to the portion ofthe insulation film 3 left under the control gate electrode CG) can berecovered. This can improve the reliability of the gate insulation film.

Then, a cleaning treatment is performed to purify the main surface ofthe semiconductor substrate 1 (Step S12 of FIG. 5). The cleaningtreatment of Step S12 is performed by using hydrofluoric acid (HF).Namely, by using dilute hydrofluoric acid (an aqueous solution ofhydrofluoric acid), the cleaning treatment of Step S12 is performed.

FIG. 11 is an essential part cross-sectional view at the stage of havingperformed the cleaning treatment of Step S12, and shows the same regions(cross-sectional regions) as those in FIGS. 6 to 10. Further, FIG. 12 isan essential part cross-sectional view at the stage after performing thecleaning treatment of Step S10, and before performing the sacrificeoxidation step of Step S11. FIG. 13 is an essential part cross-sectionalview at the stage of having performed the cleaning treatment of Step S12(the stage before performing the step of forming the insulation film 9of Step S13 described later). FIGS. 12 and 13 each show an enlarged viewof the lamination pattern 7 and the neighboring regions.

In the cleaning treatment of Step S12, a cleaning solution containinghydrofluoric acid (preferably, dilute hydrofluoric acid) is preferablyused. By using hydrofluoric acid, the silicon oxide film (oxide film)may be selectively etched. For this reason, by the cleaning treatment ofStep S12, as shown in FIG. 11, in the memory cell region 1A and theperipheral circuit region 1B, the sacrifice oxide film 8 is etched andremoved. On the other hand, in the peripheral circuit region 1B,further, the insulation film 5 (silicon oxide film) is etched andremoved. Further, as shown in FIGS. 11 and 13, in the memory cell region1A, the insulation film 5 (silicon oxide film) is side etched.Therefore, the cleaning treatment of Step S12 can also be regarded as anetching step.

By the cleaning treatment of Step S12, the sacrifice oxide film 8 isremoved. As a result, as shown in FIGS. 11 and 13, in the memory cellregion 1A, the portion of the main surface (silicon surface) of thesemiconductor substrate 1 (p type well PW1) not covered with the controlgate electrode CG, and the side surfaces (silicon surfaces of) thecontrol gate electrode CG are exposed. In the peripheral circuit region1B, the top surface (silicon surface) of the silicon film 4 is exposed.

On the other hand, in the cleaning treatment of Step S12, a cleaningsolution containing hydrofluoric acid (preferably dilute hydrofluoricacid) is used. Accordingly, the silicon film and the silicon nitridefilm are more resistant to etching than the silicon oxide film. For thisreason, in the cleaning treatment of Step S12, the semiconductorsubstrate 1, the silicon film 4, the n type silicon film 4 n, and theinsulation film 6 (silicon nitride film) are hardly etched. Namely, inthe cleaning treatment of Step S12, a cleaning solution whereby thesacrifice oxide film 8 and the insulation film 5 are more likely to beetched as compared with the semiconductor substrate 1, the silicon film4, the n type silicon film 4 n, and the insulation film 6 is used. Fromthis viewpoint, a cleaning solution containing hydrofluoric acid ispreferably used.

In the lamination pattern 7 in the memory cell region 1A, the insulationfilm 5 (silicon oxide film) is vertically sandwiched between theinsulation film 6 (silicon nitride film) and the control gate electrodeCG (n type silicon film 4 n). For this reason, in the cleaning step ofStep S12, for the insulation film 5 of the lamination pattern 7, etchingdoes not progress from the top surface side covered with the insulationfilm 6, and etching also does not progress from the bottom surface sidein contact with the control gate electrode CG. However, in the cleaningtreatment of Step S12, the sidewalls (side surfaces) 7 a and 7 b of thelamination pattern 7 are exposed to a cleaning solution containinghydrofluoric acid. Accordingly, as apparent from the comparison betweenFIG. 12 and FIG. 13, for the insulation film 5 (silicon oxide film),etching progresses from the side of the sidewalls (side surfaces) 7 aand 7 b of the lamination pattern 7, namely, from the outercircumferential side of the plane configuration of the insulation film 5toward the inner side (the side of the center of the plane configurationof the insulation film 5). In other words, in the lamination pattern 7,the insulation film 5 exposed at the sidewalls 7 a and 7 b of thelamination pattern 7 is etched (side etched) in the transversedirection, i.e., in the direction in parallel with the planar directionof the insulation film 5 (corresponding to the direction generally inparallel with the main surface of the semiconductor substrate 1).Incidentally, the direction of progress of etching of the insulationfilm 5 in the cleaning treatment of Step S12 is schematically indicatedwith an arrow (etching direction) 29 in FIG. 13. Incidentally, thesidewall 7 a and the sidewall 7 b of the lamination pattern 7 aresidewalls situated on the mutually opposing sides. On the sidewall 7 aside, the memory gate electrode MG is formed later.

However, before etching of the whole of the insulation film 5 of thelamination pattern 7, the cleaning treatment of Step S12 is terminated(stopped). Namely, in the lamination pattern 7 in the memory cell region1A, a portion (outer circumferential region of the plane configuration)of the insulation film 5 is etched and removed. However, other portionsof the insulation film 5 are not etched, and remain. This can beimplemented by controlling the hydrofluoric acid concentration of thecleaning solution and the cleaning treatment time in the cleaningtreatment of Step S12. Further, in the present embodiment, in thecleaning treatment of Step S12, it is necessary not only to remove thesacrifice oxide film 8, but also to side etch the insulation film 5. Forthis reason, as compared with the case where only the sacrifice oxidefilm 8 is removed (the case where side etching of the insulation film 5is not performed), the cleaning treatment time (wet treatment time) ismade longer.

Thus, the cleaning treatment of Step S12 is performed. As a result,although the lamination pattern 7 in the memory cell region 1A has alamination structure of the control gate electrode CG (n type siliconfilm 4 n), the insulation film 5, and the insulation film 6, theinsulation film 5 is selectively side etched. On the other hand, theperipheral circuit region 1B includes only the silicon film 4, and doesnot have the insulation film 5 and the insulation film 6. The cleaningtreatment of Step S12 is performed. As a result, the lamination pattern7 in the memory cell region 1A is in a structure in which (the sidesurfaces of) the insulation film 5 (are) is retreated (i.e., recessedinward) from (the side surfaces of) the control gate electrode CG and(the side surfaces of) the insulation film 6 at sidewalls (sidesurfaces) thereof. Therefore, the cleaning step of Step S12 can also beregarded as a step of side etching the insulation film 5 at thesidewalls of the lamination pattern 7, and allowing the insulation film5 to be retreated from (the n type silicon film 4 n forming) the controlgate electrode CG and the insulation film 6.

Then, as shown in FIG. 14, over the main surface (surface) of thesemiconductor substrate 1 (p type wells PW1 and PW2) and the sidewallsof the lamination pattern 7, the insulation film 9 for the gateinsulation film of the memory transistor is formed (Step S13 of FIG. 5).

FIG. 14 is an essential part cross-sectional view at the stage of havingperformed the formation steps of the insulation film 9 of Step S13, andshows the same regions (cross-sectional regions) as those in FIGS. 6 to11. Further, FIG. 15 is an essential part cross-sectional view at thestage of having performed the steps up to the silicon oxide film 9 aformation step (the stage before forming the silicon nitride film 9 b)out of the formation steps of the insulation film 9 of Step S13. FIG. 16is an essential part cross-sectional view of a stage of having completedthe formation steps of insulation film 9 of Step S13 (the stage ofhaving performed the steps up to the formation step of the silicon oxidefilm 9 c). FIGS. 15 and 16 each show the same regions as those in FIG.13 (i.e., an enlarged view of the lamination pattern 7 and theneighboring regions). Incidentally, in FIG. 14, for facilitatingunderstanding of the drawing, the lamination film of the silicon oxidefilm 9 a, the silicon nitride film 9 b, and the silicon oxide film 9 cis simply shown as the insulation film 9. In contrast, in FIG. 16, theinsulation film 9 is shown as the lamination film of the silicon oxidefilm 9 a, the silicon nitride film 9 b, and the silicon oxide film 9 c.In actuality, the insulation film 9 is the lamination film of thesilicon oxide film 9 a, the silicon nitride film 9 b, and the siliconoxide film 9 c.

The insulation film 9 is, as described above, an insulation film havinga charge storage part in the inside thereof. As shown in FIG. 16, theinsulation film 9 includes, as an insulation film, a lamination film(ONO film) of the silicon oxide film 9 a, the silicon nitride film 9 b,and the silicon oxide film 9 c, sequentially formed from the bottomthereof. Namely, the insulation film 9 includes a lamination film havingthe silicon oxide film (oxide film) 9 a, the silicon nitride film(nitride film) 9 b over the silicon oxide film 9 a, and the siliconoxide film (oxide film) 9 c over the silicon nitride film 9 b. In StepS13, as shown in FIGS. 14 and 16, the insulation film 9 is formed overthe surface of the p type well PW1 (however, only the portion thereofnot covered with the control gate electrode CG), over the sidewalls(side surfaces) and the top surface of the lamination pattern 7, andover the top surface of the silicon film 4 in the peripheral circuitregion 1B.

In the present embodiment, as the insulation film having a trap level,the silicon nitride film 9 b is formed. However, the insulation film isnot limited to the silicon nitride film. There may be used a high-k filmhaving a higher dielectric constant than that of a silicon nitride film,such as an aluminum oxide film (alumina), a hafnium oxide film, or atantalum oxide film. Alternatively, the insulation film may be formed ofsilicon nanodots.

Out of the insulation films 9, the silicon oxide film can be formed by,for example, an oxidation treatment (thermal oxidation treatment) or CVD(Chemical Vapor Deposition), or a combination thereof. The siliconnitride film can be formed by, for example, a CVD method.

However, in the present embodiment, the silicon oxide film 9 a formationstep is carried out by subjecting the semiconductor substrate 1 to anoxidation treatment, and preferably can be carried out by performingthermal oxidation. However, it is further preferable that the step iscarried out by ISSG oxidation.

For example, first, over the surface of the semiconductor substrate 1 (ptype well PW1), over the surfaces (side surfaces and top surface) of thelamination pattern 7, and over the surfaces (side surfaces and topsurface) of the silicon film 4, the silicon oxide film 9 a is formed bya thermal oxidation method (more preferably, ISSG oxidation) (FIG. 15corresponds to this stage). Then, over the silicon oxide film 9 a, thesilicon nitride film 9 b is deposited by a CVD method. Further, over thesilicon nitride film 9 b, the silicon oxide film 9 c is formed by a CVDmethod or thermal oxidation, or both thereof. As a result, theinsulation film 9 can be formed.

The thickness of the silicon oxide film 9 a can be set at, for example,about 3 to 6 nm. The thickness of the silicon nitride film 9 b can beset at, for example, about 5 to 10 nm. The thickness of the siliconoxide film 9 c can be set at, for example, about 4 to 7 nm. The finaloxide film (the uppermost-layer silicon oxide film 9 c of the insulationfilm 9) can be formed as a high dielectric strength film by, forexample, oxidizing the upper-layer portion of the nitride film (theintermediate-layer silicon nitride film 9 b of the insulation film 9).

The insulation film 9 functions as the gate insulation film of thememory gate electrode MG formed later, and has a charge storagefunction. Therefore, the insulation film 9 has a lamination structure ofat least three layers, wherein the potential barrier height of the innerlayer (silicon nitride film 9 b) is lower than the potential barrierheight of the outer layers (silicon oxide films 9 a and 9 c). This canbe implemented by forming the insulation film 9 as the lamination filmhaving the silicon oxide film 9 a, the silicon nitride film 9 b over thesilicon oxide film 9 a, and the silicon oxide film 9 c over the siliconnitride film 9 b as in the present embodiment.

Further, in the present embodiment, when the silicon oxide film 9 a isformed in Step S13, at the sidewalls 7 a and 7 b of the laminationpattern 7, the surfaces (exposed surfaces of) the n type silicon film 4n (forming the control gate electrode CG) are oxidized. As a result, theupper end corner portions C1 and C2 of (the n type silicon film 4 nforming) the control gate electrode CG are rounded. The reason for thisis as follows.

The lamination pattern 7 is formed by patterning the lamination film ofthe n type silicon film 4 n, the insulation film 5, and the insulationfilm 6 in the Step S8. Therefore, at the stage of having performed theStep S8, also indicated from FIG. 12, the upper end corner portions C1and C2 of the control gate electrode CG are not rounded, and are almostright-angled and sharp corner portions.

Therefore, as distinct from the present embodiment, at the sidewalls ofthe lamination pattern 7, the insulation film 5 is not side etched. Thisresults in a state in which the insulation film 5 is not retreated fromthe control gate electrode CG and the insulation film 6 (i.e., a statein which respective side surfaces of the control gate electrode CG, theinsulation film 5, and the insulation film 6 are on the same plane).When the formation step of the silicon oxide film 9 a (the oxidationtreatment of the semiconductor substrate 1) is carried out, only thesurface layer portion of each side surface of the control gate electrodeCG is oxidized. In this case, the upper end corner portions C1 and C2 ofthe control gate electrode CG are still almost right-angled and sharpcorner portions, and are not rounded.

However, in the present embodiment, in the cleaning treatment of theStep S12, at the sidewalls 7 a and 7 b of the lamination pattern 7 inthe memory cell region 1A, the insulation film 5 is side etched. Thisresults in the formation of a structure in which (the side surfaces of)the insulation film 5 (are) is retreated from (the side surfaces of) ofthe control gate electrode CG and (the side surfaces of) the insulationfilm 6. In this state, the formation step of the silicon oxide film 9 aforming the insulation film 9 (the oxidation treatment of thesemiconductor substrate 1) is performed. Namely, the insulation film 5is side etched, so that the insulation film 5 is retreated from thecontrol gate electrode CG and the insulation film 6. As a result, notonly the side surfaces of the control gate electrode CG are exposed, butalso the regions in the vicinity of the upper end corner portions C1 andC2 of the top surface of the control gate electrode CG are exposed. Inthis state, the formation step of the silicon oxide film 9 a (theoxidation treatment of the semiconductor substrate 1) is performed.Accordingly, not only the surface layer portion of each side surface ofthe control gate electrode CG, but also the regions in the vicinity ofthe upper end corner portions C1 and C2 of the top surface of thecontrol gate electrode CG are also oxidized. In this case, for the upperend corner portions C1 and C2 of the control gate electrode CG,oxidation progressed from the side surface side and the top surfaceside. As a result, the upper end corner portions C1 and C2 did notbecome almost right-angled and sharp corner portions, but becamerounded.

Thus, in the present embodiment, in the patterning step of the Step S8,the lamination pattern 7 is formed. Then, at the sidewalls of thelamination pattern 7, the insulation film 5 is side etched. Accordingly,the insulation film 5 is retreated from the control gate electrode CGand the insulation film 6. As a result, when the exposed surfaces of thecontrol gate electrode CG are oxidized later (herein, the silicon oxidefilm 9 a formation step), the upper end corner portions C1 and C2 of thecontrol gate electrode CG can be rounded.

Further, at the sidewalls of the lamination pattern 7, the insulationfilm 5 is side etched, and is retreated from the control gate electrodeCG and the insulation film 6. Then, at Step S13, the insulation film 9is formed. Accordingly, in regions in which the insulation film 5 isretreated at the sidewalls 7 a and 7 b of the lamination pattern 7 (theregions corresponding to the regions 30 a and 30 b shown in FIG. 13),portions of the insulation film 9 penetrate. Specifically, theinsulation film 9 includes a lamination film of the silicon oxide film 9a, the silicon nitride film 9 b, and the silicon oxide film 9 c.Accordingly, in regions in which the insulation film 5 is retreated atthe sidewalls 7 a and 7 b of the lamination pattern 7 (the regionscorresponding to the regions 30 a and 30 b shown in FIG. 13), portionsof the silicon nitride film 9 b also penetrate.

Further, it is preferable that the length L1 (the length L1 is shown inFIG. 13) is equal to, or larger than the thickness T4 (the thickness T4is shown in FIG. 15), where L1 denotes the length by which theinsulation film 5 is retreated from the control gate electrode CG andthe insulation film 6 at the sidewalls 7 a and 7 b of the laminationpattern 7 due to side etching of the insulation film 5 in the cleaningstep of the Step S12, and T4 denotes the thickness of the silicon oxidefilm 9 a forming the insulation film 9 formed in Step S13 (i.e., L1≧T4).The reason for this is as follows.

In the present embodiment, at the sidewalls 7 a and 7 b of thelamination pattern 7, the insulation film 5 is side etched, and isretreated from the control gate electrode CG and the insulation film 6.Then, when the silicon oxide film 9 a is formed, the exposed surfaces(surfaces of) the control gate electrode CG are oxidized. As a result,the upper end corner portions C1 and C2 of the control gate electrode CGare rounded. However, when the length L1 by which the insulation film 5is retreated from the control gate electrode CG and the insulation film6 at the sidewalls 7 a and 7 b of the lamination pattern 7 is too small,the upper end corner portions C1 and C2 of the control gate electrode CGmay not be sufficiently rounded. In contrast, the length L1 by which theinsulation film 5 is retreated from the control gate electrode CG andthe insulation film 6 at the sidewalls 7 a and 7 b of the laminationpattern 7 is set to be equal to, or larger than the thickness (formedthickness) T4 of the silicon oxide film 9 a (i.e., L1≧T4). As a result,upon oxidation of the exposed surfaces of the control gate electrode CG(herein, the silicon oxide film 9 a formation step), it is possible toform sufficiently rounded upper end corner portions C1 and C2 on thecontrol gate electrode CG. On the other hand, in the manufacturedsemiconductor device, each exposed surface of the control gate electrodeCG is retreated by ½ the film thickness T4 of the oxidized film.Therefore, it is assumed that the relationship between L1 and T4becomes: L1−T4/2T4.

Further, it is further preferable that the length L1 by which theinsulation film 5 is retreated from the control gate electrode CG andthe insulation film 6 at the sidewalls 7 a and 7 b of the laminationpattern 7 is 4 nm or more (i.e., L1≧4 nm). As a result, it is possibleto form sufficiently rounded upper end corner portions C1 and C2 on thecontrol gate electrode CG with further precision.

Further, in the present embodiment, in the silicon oxide film 9 aformation step, the exposed surfaces of the control gate electrode CGare oxidized. As a result, the upper end corner portions C1 and C2 ofthe control gate electrode CG are rounded. For this reason, in order toallow progress of oxidation of the exposed surfaces of the control gateelectrode CG, the silicon oxide film 9 a formation step is preferablyperformed not by a CVD method, but by the oxidation treatment of thesemiconductor substrate 1, and more preferably can be performed bythermal oxidation. However, it is further preferable that the step isperformed by ISSG oxidation. Further, by the step of forming the siliconoxide film 9 a, the lower end corner portions of the insulation film 6also each become in the rounded shape.

Then, as shown in FIG. 17, over the entire main surface of thesemiconductor substrate 1, namely, over the insulation film 9, in thememory cell region 1A, in such a manner as to cover the laminationpattern 7, an n type silicon film 10 n is formed (deposited) as aconductor film for memory gate electrode MG formation (Step S14 of FIG.5). Incidentally, also in FIG. 17, and subsequent FIGS. 18 to 20, andFIGS. 22 to 28, as with FIG. 14, for facilitating understanding of thedrawings, the lamination film of the silicon oxide film 9 a, the siliconnitride film 9 b, and the silicon oxide film 9 c is shown simply as theinsulation film 9.

The n type silicon film 10 n includes an n type polysilicon film (n typeimpurities-doped polysilicon film or doped polysilicon film), and can beformed by using a CVD method or the like. The film thickness (depositedfilm thickness) of the n type silicon film 10 n can be set at, forexample, about 50 to 100 nm.

Then, as shown in FIG. 18, by the anisotropic etching technology, the ntype silicon film 10 n is etched back (etched, dry etched, oranisotropically etched) by the deposited film thickness of the siliconfilm (Step S15 of FIG. 5). By the etching back step of Step S15, overboth the sidewalls 7 a and 7 b of the lamination pattern 7 (via theinsulation film 9), the n type silicon film 10 n is left in a sidewall(sidewall spacer) form, and portions of the n type silicon film 10 n inother regions are removed. This results in the formation of the memorygate electrode MG and the polysilicon spacer PS1 including the remainingportions of the n type silicon film 10 n.

At this step, out of both the sidewalls 7 a and 7 b of the laminationpattern 7, the portion of the n type silicon film 10 n left over onesidewall 7 a via insulation film 9 becomes the memory gate electrode MG;and the portion of the n type silicon film 10 n left over the othersidewall 7 b via the insulation film 9 becomes the polysilicon spacerPS1. The memory gate electrode MG and the polysilicon spacer PS1 areformed over the sidewalls on the mutually opposing sides of thelamination pattern 7, respectively, and have an almost symmetricstructure with the lamination pattern 7 sandwiched therebetween.Further, although not shown, in the forming region of a contact hole tobe coupled with the memory gate electrode MG later, the etching backstep of Step S15 is performed with this region previously covered with aphotoresist pattern. As a result, the n type silicon film 10 n is leftwithout being etched.

Incidentally, the portion of the insulation film 9 under the memory gateelectrode MG becomes the gate insulation film of the memory transistor.Thus, over the insulation film 9, the memory gate electrode MG adjacentto the control gate electrode CG via the insulation film 9 is formed.The deposited film thickness of the n type silicon film 10 n determinesthe memory gate length (gate length of the memory gate electrode MG).Therefore, by adjusting the deposited film thickness of the n typesilicon film 10 n deposited in Step S14, it is possible to adjust thememory gate length.

The memory gate electrode MG is formed by Steps S14 and S15. Therefore,the n type silicon film 10 n formation step of Step S14 and the n typesilicon film 10 n etching back step of Step S15 can also be regarded asa step of forming the memory gate electrode MG adjacent to thelamination pattern 7 via the insulation film 9 over the insulation film9.

Then, by using the photolithography technology, such a photoresistpattern (not shown) that the memory gate electrode MG is covered, andthat the polysilicon spacer PS1 is exposed is formed over thesemiconductor substrate 1. By dry etching using the photoresist patternas an etching mask, the polysilicon spacer PS1 is removed (Step S16 ofFIG. 5). Then, the photoresist pattern is removed. By the etching stepof Step S16, as shown in FIG. 19, the polysilicon spacer PS1 is removed.However, the memory gate electrode MG has been covered with thephotoresist pattern, and hence has been left without being etched.

Then, as shown in FIGS. 20 and 21, the portions of the insulation film 9not covered with the memory gate electrode MG, and exposed are removedby etching (e.g., wet etching). At this step, the portion of theinsulation film 9 situated under the memory gate electrode MG, and theportion of the insulation film 9 situated between the memory gateelectrode MG and the lamination pattern 7 are not removed, and are left.Incidentally, FIGS. 20 and 21 are each an essential part cross-sectionalview at the stage of having removed the portions of the insulation film9 not covered with the memory gate electrode MG, and exposed. FIG. 20shows the same regions (cross-sectional regions) as in FIGS. 6 to 11,FIG. 14, and FIGS. 17 to 19. FIG. 21 shows the same regions as in FIGS.12, 13, 15, and 16 (i.e., an enlarged view of the lamination pattern 7and the neighboring regions).

Then, over the silicon film 4 formed in the peripheral circuit region1B, by using the photolithography method, a photoresist pattern(although not shown herein, the photoresist pattern is formed in theentire memory cell region 1A and the p channel type MISFET formingregion of the peripheral circuit region 1B) is formed. By using thephotoresist pattern as a mask, into the silicon film 4 in the peripheralcircuit region 1B, n type impurities are introduced by an ionimplantation method or the like. As a result, in the peripheral circuitregion 1B, the n type silicon film (corresponding to the n typeimpurities-doped silicon film 4 in the peripheral circuit region 1B) isformed. Then, over the n type silicon film, using the photolithographymethod, a photoresist pattern (although not shown herein, thephotoresist pattern is formed in the entire memory cell region 1A, andthe gate electrode GE forming region of the peripheral circuit region1B) is formed. By using the photoresist pattern as an etching mask, then type silicon film is etched (dry etched), and patterned. At this step,the memory cell region 1A is covered with the photoresist pattern, andis not etched. Then, the photoresist pattern is removed. As a result, asshown in FIG. 22, the gate electrode GE including the patterned n typesilicon film (i.e., the patterned portions of the n typeimpurities-doped silicon film 4 in the peripheral circuit region 1B) isformed.

Then, using the ion implantation method, or the like, n type impuritiessuch as arsenic (As) or phosphorus (P) are introduced (doped) into thesemiconductor substrate 1 (p type wells PW1 and PW2) using thelamination pattern 7, the memory gate electrode MG, and the gateelectrode GE as ion implantation inhibiting masks. As a result, as shownin FIG. 22, n⁻ type semiconductor regions (impurity diffusion layers) 11a, 11 b, and 11 c are formed.

At this step, the n⁻ type semiconductor region 11 a is formed inself-alignment with the sidewall of the memory gate electrode MG (thesidewall on the side thereof opposite to the side adjacent to thecontrol gate electrode CG via the insulation film 9) in the memory cellregion 1A. The n⁻ type semiconductor region 11 b is formed inself-alignment with the sidewall of the control gate electrode CG (theside wall on the side thereof opposite to the side adjacent to thememory gate electrode MG via the insulation film 9) in the memory cellregion 1A. Further, the n⁻ type semiconductor regions 11 c are formed inself-alignment with opposite sidewalls of the gate electrode GE in theperipheral circuit region 1B. The n⁻ type semiconductor region 11 a andthe n⁻ type semiconductor region lib can each function as a part ofsource/drain region of the memory cell formed in the memory cell region1A. The n⁻ type semiconductor regions 11 c can each function as a partof source/drain region of the MISFET formed in the peripheral circuitregion 1B.

Then, as shown in FIG. 23, over the sidewall 7 b of the control gateelectrode CG (the sidewall 7 b on the side thereof opposite to the sideadjacent to the memory gate electrode MG via the insulation film 9),over the sidewall of the memory gate electrode MG (the sidewall on theside thereof opposite to the side adjacent to the control gate electrodeCG via the insulation film 9), and over the sidewalls (oppositesidewalls) of the gate electrode GE, the sidewall insulation films(sidewalls or sidewall spacers) SW including an insulator such assilicon oxide are formed. For example, over the entire main surface ofthe semiconductor substrate 1, an insulation film such as a siliconoxide film is deposited. The insulation film can be anisotropicallyetched (etched back), thereby to be selectively left only over thesidewalls of the control gate electrode CG, the memory gate electrodeMG, and the gate electrode GE, resulting in the formation of thesidewall insulation films SW.

Then, using the ion implantation method or the like, n type impuritiessuch as arsenic (As) or phosphorus (P) are introduced (doped) into thesemiconductor substrate 1 (p type wells PW1 and PW2) using thelamination pattern 7, the memory gate electrode MG, and the gateelectrode GE, and the sidewall insulation films SW over the sidewallsthereof as ion implantation inhibiting masks. As a result, n⁺ typesemiconductor regions (impurity diffusion layers) 12 a, 12 b, and 12 cwith a high impurity concentration are formed. At this step, the n⁺ typesemiconductor region 12 a is formed in self-alignment with the sidewallinsulation film SW over the sidewall of the memory gate electrode MG inthe memory cell region 1A. The n⁺ type semiconductor region 12 b isformed in self-alignment with the sidewall insulation film SW over thesidewall of the control gate electrode CG in the memory cell region 1A.The n⁺ type semiconductor region 12 c is formed in self-alignment withthe sidewall insulation films SW over the opposite sidewalls of the gateelectrode GE in the peripheral circuit region 1B. As a result, a LDD(lightly doped drain) structure is formed.

Thus, the n⁻ type semiconductor region 11 a, and the n⁺ typesemiconductor region 12 a having a higher impurity concentration thanthat of the region 11 a form the n type semiconductor region MSfunctioning as the source region of the memory transistor. The n⁻ typesemiconductor region 11 b, and the n⁺ type semiconductor region 12 bhaving a higher impurity concentration than that of the region 11 b formthe n type semiconductor region MD functioning as the drain region ofthe control transistor. Further, the type semiconductor regions 11 c,and the n⁺ type semiconductor regions 12 c having a higher impurityconcentration than that of the regions 11 c form the n typesemiconductor regions functioning as source/drain regions of the MISFETQn in the peripheral circuit region 1B.

Then, if required, etching (wet etching using, for example, dilutehydrofluoric acid) is performed. Thus, the top surfaces (surfaces of)the n⁺ type semiconductor regions 12 a, 12 b, and 12 c, the top surfaceof the memory gate electrode MG (the portion thereof not covered withthe sidewall insulation film SW), and the top surface of the gateelectrode GE are purified (exposed). Etching at this step can be lightetching of such a degree as to remove the natural oxide film. Then, asshown in FIG. 24, over the entire main surface of the semiconductorsubstrate 1 including over the top surfaces (surfaces of) the n⁺ typesemiconductor regions 12 a, 12 b, and 12 c, over the top surface of thememory gate electrode MG (the portion thereof not covered with thesidewall insulation film SW), and over the top surface of the gateelectrode GE, a metal film 20 is formed (deposited) in such a manner asto cover the lamination pattern 7 (control gate electrode CG), thememory gate electrode MG, the gate electrode GE, and the sidewallinsulation films SW. The metal film 20 includes, for example, a cobalt(Co) film or a nickel (Ni) film, and can be formed by using a sputteringmethod or the like.

Then, the semiconductor substrate 1 is subjected to a heat treatment.Accordingly, the top layer portions (surface layer portions) of the n⁺type semiconductor regions 12 a, 12 b, and 12 c, the memory gateelectrode MG, and the gate electrode GE are allowed to react with themetal film 20. As a result, as shown in FIG. 25, at the tops (the topsurfaces, surfaces, or top layer parts) of the n⁺ type semiconductorregions 12 a, 12 b, and 12 c, the memory gate electrode MG, and the gateelectrode GE, metal silicide layers (metal silicide films) 21 areformed, respectively. The metal silicide layer 21 can be, for example, acobalt silicide layer (when the metal film 20 is a cobalt film) or anickel silicide layer (when the metal film 20 is a nickel film). Then,the unreacted portions of the metal film 20 are removed. FIG. 25 shows across-sectional view at this stage. Thus, by performing a so-calledsalicide process, the tops of the n⁺ type semiconductor regions 12 a, 12b, and 12 c, the memory gate electrode MG, and the gate electrode GE,the metal silicide layers 21 are formed. As a result, it is possible tolower the resistances of the source, the drain, and the memory gateelectrode MG.

In the salicide process, with the top surface of (the n type siliconfilm 10 n forming) the memory gate electrode MG in contact with themetal film 20, the heat treatment is performed. Accordingly, the toplayer part of (the n type silicon film 10 n forming) the memory gateelectrode MG reacts with the metal film 20. As a result, at the top (topsurface) of (the n type silicon film 10 n forming) the memory gateelectrode MG, the metal silicide layer 21 is formed. However, over thecontrol gate electrode CG, the insulation films 5 and 6 are formed.Thus, the top surface of (the n type silicon film 4 n forming) thecontrol gate electrode CG is not in contact with the metal film 20, andthe insulation films 5 and 6 interpose therebetween. Accordingly, (the ntype silicon film 4 n forming) the control gate electrode CG does notreact with the metal film 20. For this reason, over the control gateelectrode CG, the metal silicide layer 21 is not formed.

Then, as shown in FIG. 26, over the entire main surface of thesemiconductor substrate 1, an insulation film 22 is formed (deposited)in such a manner as to cover the lamination pattern 7, the memory gateelectrode MG, the gate electrode GE, and the sidewall insulation filmsSW. Over the insulation film 22, an insulation film 23 is formed(deposited). Then, if required, using a CMP (Chemical MechanicalPolishing) method, or the like, the top surface of the insulation film23 is planarized.

The insulation film 22 preferably includes a silicon nitride film. Theinsulation film 23 over the insulation film 22 preferably includes asilicon oxide film or the like. These can be respectively formed using aCVD method or the like. The film thickness of the insulation film 22 issmaller than the film thickness of the insulation film 23. The thickinsulation film 23 functions as an interlayer insulation film. The thininsulation film (silicon nitride film) 22 functions as an etchingstopper film for forming contact holes in the insulation film 23.

Then, as shown in FIG. 27, using a photolithography method, using aphotoresist pattern (not shown) formed over the insulation film 23 as anetching mask, the insulation film 23 and the insulation film 22 are dryetched. As a result, in the insulation films 22 and 23, contact holes(openings or through holes) CNT are formed. For forming the contactholes CNT, first, the insulation film 23 is dry etched. The insulationfilm 22 is allowed to function as an etching stopper film. Then,portions of the insulation film 22 at the bottoms of the contact holesCNT are removed by dry etching. Thus, the contact holes CNT penetratingthrough the insulation films 22 and 23 are formed. Thus, the insulationfilm 22 is allowed to function as an etching stopper for etching theinsulation film (interlayer insulation film) 23. This can avoid damagingof the underlying layer due to excessive boring thereof, anddeterioration of the processing dimension precision when the contactholes CNT are formed by etching.

The contact holes CNT are formed in the tops of the n⁺ typesemiconductor regions 12 a, 12 b, and 12 c, the control gate electrodeCG, the memory gate electrode MG, the gate electrode GE, and the like.At the bottoms of the contact holes CNT, there are exposed portions ofthe main surface of the semiconductor substrate 1 such as portions of(the metal silicide layers 21 over the surfaces of) the n⁺ typesemiconductor regions 12 a, 12 b, and 12 c, a portion of the controlgate electrode CG, a portion of (the metal silicide layer 21 over thesurface of) the memory gate electrode MG or (the metal silicide layer 21over the surface of) the gate electrode GE, and the like. Incidentally,in the cross-sectional view of FIG. 27, there is shown a cross sectionin which portions of (the metal silicide layers 21 over the surfaces of)the n⁺ type semiconductor regions 12 b and 12 c are exposed at thebottoms of the contact holes CNT.

Then, in each contact hole CNT, a conductive plug (conductor part forcoupling) PG including tungsten (W) or the like is formed. In order toform the plug PG, the following procedure is performed. For example,over the insulation film 23 including the inside (over the bottom andthe sidewall) of the contact hole CNT, a barrier conductor film (e.g., atitanium film, a titanium nitride film, or a lamination film thereof) isformed. Then, over the barrier conductor film, a main conductor filmincluding a tungsten film or the like is formed in such a manner as tofill the contact hole CNT. The unnecessary portions of the mainconductor film and the barrier conductor film over the insulation film23 are removed by a CMP method, an etching back method, or the like. Asa result, the plug PG can be formed. Incidentally, for simplification ofthe drawing, in FIG. 27, the barrier conductor film and the mainconductor film (tungsten film) forming the plug PG are shown in anintegral form.

Then, as shown in FIG. 28, over the insulation film 23 including theplug PG embedded therein, a stopper insulation film (insulation film foretching stopper) 24 and an insulation film for wire formation(interlayer insulation film) 25 are successively formed. The stopperinsulation film 24 is a film serving as an etching stopper forprocessing grooves in the insulation film 25. A material having anetching selectivity with respect to the insulation film 25 is used. Forexample, the stopper insulation film 24 can be a silicon nitride film,and the insulation film 25 can be a silicon oxide film.

Then, with a single damascene method, a first-layer wire M1 is formed.First, by dry etching using a photoresist pattern (not shown) as a mask,in predetermined regions of the insulation film 25 and the stopperinsulation film 24, wire grooves 26 are formed. Then, over the mainsurface of the semiconductor substrate 1 (i.e., over the insulation film25 including over the bottoms and the sidewalls of the wire grooves 26),a barrier conductor film (e.g., a titanium nitride film, a tantalumfilm, or a tantalum nitride film) is formed. Subsequently, by a CVDmethod, a sputtering method, or the like, over the barrier conductorfilm, a seed layer of copper is formed. Further, using an electrolyticplating method or the like, a copper plating film is formed over theseed layer. Thus, the copper plating film fills the inside of each wiregroove 26. Then, portions of the copper plating film, the seed layer,and the barrier metal film in regions except for the insides of the wiregrooves 26 are removed by a CMP method. As a result, the first-layerwire M1 including copper as a main conductive material is formed.Incidentally, for simplification of the drawing, in FIG. 28, the copperplating film, the seed layer, and the barrier conductor film forming thewire M1 are shown in an integral form.

The wires M1 are electrically coupled via the plugs PG to the sourceregion (semiconductor region MS) of the memory transistor, the drainregion (semiconductor region MD) of the control transistor, thesource/drain regions (n⁺ type semiconductor regions 12 c) of the MISFETQn in the peripheral circuit region 1B, the control gate electrode CG,the memory gate electrode MG, the gate electrode GE, or the like. Then,by a dual damascene method or the like, second- and more-layer wires areformed. However, herein, they are not shown, and a description thereonwill be omitted. Further, the wires M1 and upper-layer wires are notlimited to damascene wires, and can also be formed by patterning theconductor film for wiring. For example, the wires may be tungsten wiresor aluminum wires.

Then, the effects of the present embodiment will be described in moredetails.

FIG. 29 is an essential part cross-sectional view of a semiconductordevice of First Comparative Example. FIG. 30 is an essential partcross-sectional view of a semiconductor device of Second ComparativeExample. They respectively correspond to FIG. 2 of the presentembodiment.

The semiconductor device of First Comparative Example shown in FIG. 29is a semiconductor device having a memory cell of a nonvolatile memory.Over the top of a p type well 101 of the semiconductor substrate, acontrol gate electrode CG101 and a memory gate electrode MG101 formingthe nonvolatile memory cell are formed in such a manner as to beadjacent to each other. Then, between the control gate electrode CG101and the p type well PW101, an insulation film 103 as the gate insulationfilm is formed. Whereas, between the memory gate electrode MG101 and thep type well PW101, and between the control gate electrode CG101 and thememory gate electrode MG101, an insulation film 109 including alamination film of a silicon oxide film 109 a, a silicon nitride film109 b, and a silicon oxide film 109 c is formed. The control gateelectrode CG101 and the memory gate electrode MG101 each include asilicon film. Over the top of the control gate electrode CG101 and thetop of the memory gate electrode MG101, a metal salicide layer 121 isformed by a salicide process.

The semiconductor device of such a structure of First ComparativeExample has the following problems.

Namely, in the semiconductor device of First Comparative Example shownin FIG. 29, the metal silicide layer 121 over the control gate electrodeCG101 and the metal silicide layer 121 over the memory gate electrodeMG101 are insulated and isolated from each other by the insulation film109 which is an ONO film. However, the film thickness of the insulationfilm 109 is small. As a result, the end of the metal silicide layer 121over the control gate electrode CG101 is close to the end of the metalsilicide layer 121 over the memory gate electrode MG101. This may causea short-circuit failure between the control gate electrode CG101 and thememory gate electrode MG101. The short circuit between the control gateelectrode CG101 and the memory gate electrode MG101 depends upon theformation state of the metal silicide layers 121 over the control gateelectrode CG101 and the memory gate electrode MG101. Thus, the shortcircuit is caused by the proximity between the metal silicide layer 121over the control gate electrode CG101 and the metal silicide layer 121over the memory gate electrode MG101 with the thin insulation film 109interposed therebetween. The semiconductor devices which have undergonesuch a short-circuit failure are required to be selected and excluded bythe inspection of manufacturing of the semiconductor devices, resultingin a reduction of the manufacturing yield of semiconductor devices, andan increase in cost (unit cost) of the semiconductor devices.

The semiconductor device of Second Comparative Example shown in FIG. 30is a semiconductor device having a memory cell of a nonvolatile memory.Over the top of a p type well 201 of the semiconductor substrate, alamination pattern 207 including a control gate electrode CG201 and aninsulation film 206 thereover, and a memory gate electrode MG201 areformed in such a manner as to be adjacent to each other. Then, betweenthe control gate electrode CG201 and the p type well PW201, aninsulation film 203 as the gate insulation film is formed. Whereas,between the memory gate electrode MG201 and the p type well PW201, andbetween the lamination pattern 207 and the memory gate electrode MG201,an insulation film 209 including a lamination film of a silicon oxidefilm 209 a, a silicon nitride film 209 b, and a silicon oxide film 209 cis formed. The control gate electrode CG201 and the memory gateelectrode MG201 each include a silicon film. Over the top of the memorygate electrode MG201, a metal silicide layer 221 is formed by a salicideprocess. On the other hand, over the control gate electrode CG201, thereis the insulation film 206, and hence the metal silicide layer 221 isnot formed.

The insulation film 206 is formed of, for example, a silicon nitridefilm. This is for the following reason. The steps after the formation ofthe lamination pattern 207 include steps using hydrofluoric acid.Therefore, when the insulation film 206 is formed of a silicon oxidefilm, the insulation film 206 may become too small. In SecondComparative Example shown in FIG. 30, as distinct from the structure ofFIGS. 1 and 2, the semiconductor device does not have a structure inwhich such an insulation film (e.g., a silicon oxide film) as to beretreated by a dilute hydrofluoric acid treatment is interposed betweenthe control gate electrode CG201 and the insulation film 206. Therefore,the side surface of the lamination pattern 207 is in a recess-free andalmost linear shape. Namely, the upper end corner portion of the controlgate electrode CG201 is more angular than that of the structure (controlgate electrode CG) of FIGS. 1 and 2.

Further, in the semiconductor device of Second Comparative Example shownin FIG. 30, over the control gate electrode CG201, there is theinsulation film 206. Therefore, the metal silicide layer 221 is formedover the top of the memory gate electrode MG201, but is not formed overthe top of the control gate electrode CG201. This prevents the metalsilicide layer 221 over the memory gate electrode MG201 from being closeto the control gate electrode CG201 with the thin insulation film 209interposed therebetween. For this reason, it is possible to prevent theoccurrence of the short-circuit failure between the control gateelectrode CG201 and the memory gate electrode MG201.

However, the semiconductor device of Second Comparative Example has thefollowing problems.

Namely, the control gate electrode CG201 and the memory gate electrodeMG201 are adjacent to each other via the thin insulation film 209interposed therebetween. This raises a fear of the leakage currentbetween the control gate electrode CG201 and the memory gate electrodeMG201. Particularly, at the sidewall on the side of the laminationpattern 207 adjacent to the memory gate electrode MG201, the upper endcorner portion C201 of the control gate electrode CG201 is almostright-angled, and sharp. Accordingly, the electric field concentrates tothe upper end corner portion C201. As a result, a leakage currentbecomes more likely to occur between the upper end corner portion C201of the control gate electrode CG201 and the memory gate electrode MG201(or the metal silicide layer 221 over the memory gate electrode MG201).

Further, in the ion implantation step for forming the source/drainregions, impurities to be ion-implanted are also introduced into the topof the insulation film 209 situated between the lamination pattern 207and the memory gate electrode MG201 (e.g., a portion of the insulationfilm 209 in a region 231 surrounded by a dotted line of FIG. 30). Theimpurities-doped portion of the insulation film 209 (the portion of theinsulation film 209 in the region 231) is a region in which the leakagecurrent is more likely to occur than in other portions of the insulationfilm 209. Thus, a leakage current becomes more likely to occur via theregion (the portion of the insulation film 209 in the region 231)between the upper end corner portion C201 of the control gate electrodeCG201 and the memory gate electrode MG201 (or the metal silicide layer221 over the memory gate electrode MG201).

The leakage current between the control gate electrode CG201 and thememory gate electrode MG201 reduces the performances of thesemiconductor device having a nonvolatile memory. For this reason, theleakage current as described above is desirably minimized.

In contrast, in the present embodiment, as also shown in FIGS. 1 and 2,at the sidewall 7 a on the side of the lamination pattern 7 adjacent tothe memory gate electrode MG, the upper end corner portion C1 of thecontrol gate electrode CG is not sharp, but is rounded (is roundish, orhas a round shape).

The control gate electrode CG is adjacent to the memory gate electrodeMG via the thin insulation film 9. When a potential difference occursbetween the control gate electrode CG and the memory gate electrode MG,the electric field may concentrate to the upper end corner portion C1 ofthe control gate electrode CG. However, in the present embodiment, theupper end corner portion C1 of the control gate electrode CG is rounded.As a result, the electric field concentration at the upper end cornerportion C1 of the control gate electrode CG can be relieved (inhibitedor reduced). For this reason, the leakage current can be inhibited orprevented from occurring between the upper end corner portion C1 of thecontrol gate electrode CG and the memory gate electrode MG (or the metalsilicide layer 21 over the top of the memory gate electrode MG).

Further, in the ion implantation step for forming the n⁻ typesemiconductor regions 11 a and 11 b, or in the ion implantation step forforming the n⁺ type semiconductor regions 12 a and 12 b, impurities tobe ion-implanted are also introduced into the top of the insulation film9 situated between the lamination pattern 7 and the memory gateelectrode MG (e.g., a portion of the insulation film 9 in a region 31surrounded by a dotted line of FIG. 2). The impurities-doped portion ofthe insulation film 9 (the portion of the insulation film 9 in theregion 31) is a region in which the leakage current is more likely tooccur than in other portions of the insulation film 9. However, in thepresent embodiment, the upper end corner portion C1 of the control gateelectrode CG is rounded. Accordingly, as compared with the case wherethe upper end corner portion C1 is not rounded but is right-angled, theupper end corner portion C1 of the control gate electrode CG can beseparated (made distant) from the impurities-doped portion of theinsulation film 9 (the portion of the insulation film 9 in the region31). Namely, the length between the upper end corner portion C1 of thecontrol gate electrode CG and the impurities-doped portion of theinsulation film 9 (the portion of the insulation film 9 in the region31) can be set large. This can inhibit or prevent the leakage currentfrom occurring via the impurities-doped portion of the insulation film 9(the portion of the insulation film 9 in the region 31) between theupper end corner portion C1 of the control gate electrode CG and thememory gate electrode MG (or the metal silicide layer 21 over the memorygate electrode MG).

Thus, in the present embodiment, at the sidewall 7 a on the side of thelamination pattern 7 adjacent to the memory gate electrode MG, the upperend corner portion C1 of the control gate electrode CG is not sharp, butis rounded. This can inhibit or prevent the leakage current between thecontrol gate electrode CG and the memory gate electrode MG. As a result,it is possible to improve the performances of the semiconductor devicehaving a nonvolatile memory.

Further, in the present embodiment, over the control gate electrode CG,the insulation film 5 and the insulation film 6 are stacked to form thelamination pattern 7. Accordingly, the metal silicide layer 21 is formedover the top of the memory gate electrode MG, but is not formed over thetop of the control gate electrode CG. This prevents the metal silicidelayer 21 over the memory gate electrode MG from being close to thecontrol gate electrode CG with the thin insulation film 9 interposedtherebetween. For this reason, it is possible to prevent the occurrenceof the short-circuit failure between the control gate electrode CG andthe memory gate electrode MG. Therefore, it is possible to improve themanufacturing yield of the semiconductor devices. Further, it ispossible to reduce the cost (unit cost) of the semiconductor devices.Still further, it is possible to improve the reliability of thesemiconductor device.

FIG. 31 is a graph showing the leakage current between the memory gateelectrode and the control gate electrode of the nonvolatile memory. Theabscissa of the graph of FIG. 31 corresponds to the leakage currentvalue upon applying a predetermined voltage across the memory gateelectrode and the control gate electrode; and the ordinate of the graphof FIG. 31 corresponds to the cumulative frequency (cumulative frequencyindicated with standard deviation σ). Further, in FIG. 31, the caseindicated with “First Comparative Example” is the case of the structureof First Comparative Example shown in FIG. 29. In FIG. 31, the caseindicated with “Present Embodiment” is the case of the structure of thepresent embodiment shown in FIGS. 1 and 2.

As shown in the graph of FIG. 31, as compared with the structure ofFirst Comparative Example shown in FIG. 29, the structure of the presentembodiment shown in FIGS. 1 and 2 can more largely reduce the leakagecurrent between the control gate electrode CG and the memory gateelectrode MG. Further, although not shown in the graph of FIG. 31, thefollowing has been confirmed: in the case of the structure of SecondComparative Example shown in FIG. 30, the value of the leakage currentis a value between that in “First Comparative Example” and that in“Present Embodiment” in FIG. 31.

Further, in the present embodiment, over the control gate electrode CG,the insulation films 5 and 6 are stacked to form the lamination pattern7. At the sidewall 7 a on the side of the lamination pattern 7 adjacentto the memory gate electrode MG, the insulation film 5 is retreated fromthe control gate electrode CG and the insulation film 6. As a result,the upper end corner portion C1 of the control gate electrode CG can berounded.

Namely, as distinct from the present embodiment, unless the insulationfilm 5 is retreated from the control gate electrode CG and theinsulation film 6 at the sidewall of the lamination pattern 7, even whenthe exposed surface of (the n type silicon film 4 n forming) the controlgate electrode CG is oxidized, it is difficult to round the upper endcorner portion C1 of the control gate electrode CG. In contrast, as inthe present embodiment, there is formed a state (the structure of FIG.13) in which at the sidewall of the lamination pattern 7, the insulationfilm 5 is retreated from the control gate electrode CG and theinsulation film 6. As a result, by subsequently oxidizing the exposedsurface of (the n type silicon film 4 n forming) the control gateelectrode CG (in the case of the present embodiment, oxidizing theexposed surface in the silicon oxide film 9 a formation step), it ispossible to round the upper end corner portion C1 of the control gateelectrode CG as in FIG. 15.

Accordingly, the following state results: in the memory cell MC in thesemiconductor device after manufacturing, at the sidewall 7 a on theside of the lamination pattern 7 adjacent to the memory gate electrodeMG, the insulation film 5 is retreated from the control gate electrodeCG and the insulation film 6, and the upper end corner portion C1 of thecontrol gate electrode CG is rounded.

Further, in the patterning step of the Step S8, the lamination pattern 7is formed. Then, at the sidewall of the lamination pattern 7, theinsulation film 5 is side etched, and is retreated from the n typesilicon film 4 n (control gate electrode CG) and the insulation film 6.Thus, it is possible to form the state (the structure of FIG. 13) inwhich the insulation film 5 is retreated from the control gate electrodeCG and the insulation film 6 with ease and precision.

Then, it is preferable that the insulation film 5 is a silicon oxidefilm, and that the insulation film 6 is a silicon nitride film. As aresult, it becomes possible to selectively side etch the insulation film5 with precision. Further, in the patterning step of the Step S8, thelamination pattern 7 is formed. Then, at the sidewall of the laminationpattern 7, the insulation film 5 is side etched, and retreated from (then type silicon film 4 n forming) the control gate electrode CG and theinsulation film 6. This procedure is more preferably carried out by awet treatment using hydrofluoric acid (in the case of the presentembodiment, corresponding to the cleaning treatment of the Step S12). Asa result, it is possible to side etch the insulation film 5 includingsilicon oxide with more precision while preventing etching of theinsulation film 6 and the control gate electrode CG.

Further, in the present embodiment, in order to reduce the leakagecurrent between the control gate electrode CG and the memory gateelectrode MG, the upper end corner portion C1 of the control gateelectrode CG is rounded. However, when the lower end corner portion C3of the control gate electrode CG is too rounded, the function of thecontrol gate electrode CG may be adversely affected thereby. Herein, thelower end corner portion C3 of the control gate electrode CG correspondsto the corner portion between the bottom surface of the control gateelectrode CG (the surface thereof in contact with the insulation film3), and the side surface on the side of the control gate electrode CGadjacent to the memory gate electrode MG (the side surface thereofcorresponding to the sidewall 7 a). Accordingly, it is preferable that,at the sidewall 7 a on the side of the lamination pattern 7 adjacent tothe memory gate electrode MG, the degree of roundness of the upper endcorner portion C1 of the control gate electrode CG is larger than thedegree of roundness of the lower end corner portion C3 of the controlgate electrode CG. Then, it is further preferable that, at the sidewall7 a on the side of the lamination pattern 7 adjacent to the memory gateelectrode MG, the lower end corner portion C3 of the control gateelectrode CG is not rounded, namely, is roughly right-angled. With thisconfiguration, the degree of roundness of the upper end corner portionC1 of the control gate electrode CG is enhanced. As a result, it ispossible to reduce the leakage current between the control gateelectrode CG and the memory gate electrode MG. In addition, the degreeof roundness of the lower end corner portion C3 of the control gateelectrode CG is lowered. As a result, it is possible to acquire thefunction of the control gate electrode CG with more precision. Herein,the respective degrees of roundness of the upper end corner portion C1and the lower end corner portion C3 of the control gate electrode CGcorrespond to their respective corner Rs (radiuses of the roundedportion) of the upper end corner portion C1 and the lower end cornerportion C3 of the control gate electrode CG, respectively.

Further, at the sidewall of the lamination pattern 7, the insulationfilm 5 is side etched, and is retreated from (the n type silicon film 4n forming) the control gate electrode CG and the insulation film 6. Atthis step, the insulation film 3 situated under the control gateelectrode CG is preferably etched (side etched) as little as possiblebecause it is used as the gate insulation film later. From thisviewpoint, the thickness (formed film thickness) T2 of the insulationfilm 5 formed in the Step S6 is preferably larger than the thickness(formed film thickness) T1 of the insulation film 3 formed in the StepS4 (i.e., T2>T1). This can inhibit or prevent the insulation film 3situated under the control gate electrode CG from being etched (sideetched) when the insulation film 5 is side etched, and is retreated from(the n type silicon film 4 n forming) the control gate electrode CG andthe insulation film 6. As a result, it is possible to more improve thereliability of the insulation film 3 functioning as the gate insulationfilm.

Further, as the insulation film 3 formed in the Step S4, either of asilicon oxide film or a silicon oxynitride film can be used. However, asilicon oxynitride film is more preferably used as the insulation film3. In the case where both of the insulation film 5 and the insulationfilm 3 are silicon oxide films, when the insulation film 5 is sideetched, and is retreated from the control gate electrode CG and theinsulation film 6, the insulation film 3 under the control gateelectrode CG tends to be etched (side etched). However, when theinsulation film 3 is a silicon oxynitride film, the insulation film 3under the control gate electrode CG can be more precisely prevented frombeing etched (side etched) upon side etching of the insulation film 5.Further, when a silicon oxide film formed by a CVD method is used as theinsulation film 5, the insulation film 5 can be more precisely etchedwhile preventing etching (side etching) of the insulation film 3 underthe control gate electrode CG.

Further, in the present embodiment, when the sacrifice oxide film 8 isremoved in the cleaning step of Step S12, at the sidewalls 7 a and 7 bof the lamination pattern 7, the insulation film 5 is side etched. Forthis reason, it is not necessary to separately add a side etching stepof the insulation film 5. This can inhibit the increase in number ofmanufacturing steps of the semiconductor device.

Further, in the following Embodiment 2, when a natural oxide film, andthe like are removed in the cleaning step of Step S10 a, at thesidewalls 7 a and 7 b of the lamination pattern 7, the insulation film 5is side etched. For this reason, it is not necessary to separately add aside etching step of the insulation film 5. This can inhibit theincrease in number of manufacturing steps of the semiconductor device.

Embodiment 2

In Embodiment 2, a description will be given to another manufacturingprocess for manufacturing the semiconductor device described in theEmbodiment 1.

FIGS. 32 to 40 are each an essential part cross-sectional view of thesemiconductor device of the present embodiment during a manufacturingstep. Out of these, FIGS. 32, 35, 37 and 39 show the same regions(cross-sectional regions) as those in FIGS. 6 to 11, 14, 17 to 20, and22 to 28 of the Embodiment 1. FIGS. 33, 34, 36, 38, and 40 show the sameregions (cross-sectional regions) as those in FIGS. 12, 13, 15, 16, and21 of the Embodiment 1.

In the Embodiments 1 and 2, in the Step S8, the lamination pattern 7 isformed. Then, there is performed a step in which, at the sidewalls ofthe lamination pattern 7, the insulation film 5 is side etched, and theinsulation film 5 is retreated from (the n type silicon film 4 nforming) the control gate electrode CG and the insulation film 6. Thisstep corresponds to the cleaning step of Step S12 in the Embodiment 1,and corresponds to the cleaning step of Step S10 in the presentembodiment. Below, manufacturing steps of the semiconductor device ofthe present embodiment will be described by reference to theaccompanying drawings.

The manufacturing steps of the present embodiment are the same in thesteps up to immediately before performing the cleaning step of the StepS10 as the manufacturing steps of Embodiment 1. Therefore, herein, adescription thereon will be omitted, and the steps will be describedfrom the cleaning step of Step S10.

The same steps as Steps S1 to S9 of Embodiment 1 are performed to obtainthe structure of FIG. 9. Then, also in the present embodiment, thecleaning treatment of Step S10 (cleaning step) is performed. FIG. 32shows an essential part cross-sectional view at the stage of havingperformed the cleaning treatment of Step S10 in the present embodiment.Further, FIGS. 33 and 34 each show an enlarged view of the laminationpattern 7 and the neighboring regions, wherein FIG. 33 shows the stageimmediately before performing the cleaning treatment of Step S10, andFIG. 34 shows the stage of having performed the cleaning treatment ofStep S10 (the stage before performing the sacrifice oxidation of StepS11).

Embodiment 1 and the present embodiment are different in the cleaningsolution for use in the cleaning treatment of Step S10. Namely, inEmbodiment 1, for the cleaning treatment of Step S10, a cleaningsolution not containing hydrofluoric acid was used. In contrast, in thepresent embodiment, for the cleaning treatment of Step S10, hydrofluoricacid (HF) is used. Thus, using a cleaning solution containinghydrofluoric acid (HF), the cleaning treatment of Step S10 is performed.Specifically, in the present embodiment, using dilute hydrofluoric acid(an aqueous solution of hydrofluoric acid), the cleaning treatment ofStep S10 is performed. Below, the cleaning treatment of Step S10(cleaning step) performed in the present embodiment is referred to asthe cleaning treatment of Step S10 a (cleaning step).

In the present embodiment, in the cleaning treatment of Step S10 a, byusing a cleaning solution containing hydrofluoric acid (preferablydilute hydrofluoric acid), the silicon oxide film can be selectivelyetched. Accordingly, by the cleaning treatment of Step S10 a, as shownin FIGS. 32 and 34, in the lamination pattern 7 in the memory cellregion 1A, the insulation film 5 (silicon oxide film) is side etched.Further, when over the surface of the p type well PW1, and the like, anatural oxide film is formed, the natural oxide film can also be removedby the cleaning treatment of Step S10 a. Therefore, the cleaning step ofStep S10 a of the present embodiment can also be regarded as an etchingstep.

By the cleaning treatment of Step S10 a, as shown in FIGS. 32 and 34, inthe memory cell region 1A, portions of the main surface (siliconsurface) of the semiconductor substrate 1 (p type well PW1) not coveredwith the control gate electrode CG, and the side surfaces (siliconsurfaces of) the control gate electrode CG are exposed. In theperipheral circuit region 1B, the top surface (silicon surface) of thesilicon film 4 is exposed.

On the other hand, in the cleaning step of Step S10 a, a cleaningsolution containing hydrofluoric acid (preferably dilute hydrofluoricacid) is used. Therefore, the silicon film and the silicon nitride filmare less likely to be etched than the silicon oxide film. Accordingly,in the cleaning treatment of Step S10 a, the semiconductor substrate 1,the silicon film 4, the n type silicon film 4 n, and the insulation film6 (silicon nitride film) are hardly etched. Namely, in the cleaningtreatment of Step S10 a, a cleaning solution whereby the insulation film5 is more likely to be etched as compared with the semiconductorsubstrate 1, the silicon film 4, the n type silicon film 4 n, and theinsulation film 6 is used. From this viewpoint, a cleaning solutioncontaining hydrofluoric acid is preferably used.

In the lamination pattern 7 in the memory cell region 1A, the insulationfilm 5 (silicon oxide film) is vertically sandwiched between theinsulation film 6 (silicon nitride film) and the control gate electrodeCG (n type silicon film 4 n). For this reason, in the cleaning step ofStep S10 a, for the insulation film 5 of the lamination pattern 7,etching does not progress from the top surface side covered with theinsulation film 6, and etching also does not progress from the bottomsurface side in contact with the control gate electrode CG. However, inthe cleaning treatment of Step 10 a, the sidewalls (side surfaces of)the lamination pattern 7 are exposed to a cleaning solution containinghydrofluoric acid. Accordingly, as apparent from the comparison betweenFIG. 33 and FIG. 34, in the lamination pattern 7, the insulation film 5exposed at the sidewalls (side surfaces) of the lamination pattern 7 isetched (side etched) in the transverse direction, i.e., in the directionin parallel with the planar direction of the insulation film 5(corresponding to the direction generally in parallel with the mainsurface of the semiconductor substrate 1).

However, before etching of the whole of the insulation film 5 of thelamination pattern 7, the cleaning treatment of Step S10 a is terminated(stopped). Namely, in the lamination pattern 7 in the memory cell region1A, a portion (outer circumferential region of the plane configuration)of the insulation film 5 is etched and removed. However, other portionsof the insulation film 5 are not etched, and remain. This can beimplemented by controlling the hydrofluoric acid concentration of thecleaning solution and the cleaning treatment time in the cleaningtreatment of Step S10 a. Further, in the present embodiment, in thecleaning treatment of Step S10 a, it is necessary not only to remove thenatural oxide film, but also to side etch the insulation film 5. Forthis reason, as compared with the case where only the natural oxide filmis removed (the case where side etching of the insulation film 5 is notperformed), the cleaning treatment time (wet treatment time) is madelonger.

Thus, the cleaning treatment of Step S10 a is performed. As a result,although the lamination pattern 7 in the memory cell region 1A has alamination structure of the control gate electrode CG (n type siliconfilm 4 n), the insulation film 5, and the insulation film 6, theinsulation film 5 is selectively side etched. On the other hand, in theperipheral circuit region 1B, the insulation film 5 is etched, so thatonly the silicon film 4 remains. The cleaning treatment of Step S12 isperformed. As a result, the lamination pattern 7 in the memory cellregion 1A is in a structure in which (the side surfaces of) theinsulation film 5 (are) is retreated (i.e., recessed inward) from (theside surfaces of) the control gate electrode CG and (the side surfacesof) the insulation film at sidewalls (side surfaces). Therefore, thecleaning step of Step S10 a can also be regarded as a step of sideetching the insulation film 5 at the sidewalls of the lamination pattern7, and allowing the insulation film 5 to be retreated from (the n typesilicon film 4 n forming) the control gate electrode CG and theinsulation film 6.

Then, also in the present embodiment, by performing the same sacrificeoxidation of Step S11 as that in Embodiment 1, the sacrifice oxide film8 is formed. FIG. 35 shows an essential part cross-sectional view at thestage of having performed the sacrifice oxidation of Step S11 in thepresent embodiment. Further, FIG. 36 shows an enlarged view of thelamination pattern 7 and the neighboring regions at the same stage asthat in FIG. 35 (the stage of having performed sacrifice oxidation ofStep S11).

The sacrifice oxidation of Step S11 to be performed in the presentembodiment is basically the same as the sacrifice oxidation of Step S11to be performed in Embodiment 1. However, the present embodiment isdifferent from Embodiment 1 in the following point: the sacrificeoxidation of Step S11 is performed with the top surface of the siliconfilm 4 used for forming (patterning) the gate electrode GE later exposedin the peripheral circuit region 1B; and accordingly, as shown in FIG.35, the sacrifice oxide film 8 is also formed over the top surface ofthe silicon film 4 in the peripheral circuit region 1B. Further, thepresent embodiment is also different from Embodiment 1 in the followingpoint: the sacrifice oxidation of Step S11 is performed with theinsulation film 5 side etched in the lamination pattern 7 in the memorycell region 1A. Below, the sacrifice oxidation of Step S11 (sacrificeoxidation step) to be performed in the present embodiment is referred toas sacrifice oxidation of step S11 a (sacrifice oxidation step).

By sacrifice oxidation of Step S11 a, as shown in FIGS. 35 and 36, inthe memory cell region 1A, portions of the main surface (surface) of thesemiconductor substrate 1 (p type well PW1) not covered with thelamination pattern 7 (control gate electrode GE), and the side surfaces(sidewalls) of (the n type silicon film 4 n forming) the control gateelectrode CG of the lamination pattern 7 are oxidized to form thesacrifice oxide film (silicon oxide film) 8. Whereas, in the peripheralcircuit region 1B, the top surface of the silicon film 4 is oxidized toform the sacrifice oxide film (silicon oxide film) 8. The film thicknessof the sacrifice oxide film 8 can be set at, for example, about 3 to 6nm. When the sacrifice oxidation of Step S11 a is performed by ISSGoxidation, not only the Si region (herein, the semiconductor substrate1, the n type silicon film 4 n, and the silicon film 4) but also the SiNregion (herein the insulation film 6) can be oxidized. Accordingly, thetop surface and the side surfaces (sidewalls) of the insulation film 6(silicon nitride film) of the lamination pattern 7 are also oxidized toform the sacrifice oxide film 8.

In the present embodiment, when the sacrifice oxide film 8 is formed inthe sacrifice oxidation step of Step S11 a, at the sidewalls of thelamination pattern 7, the surfaces (exposed surfaces of) the n typesilicon film 4 n forming the gate electrode CG (are) is oxidized. As aresult, the upper end corner portions C1 and C2 of (the n type siliconfilm 4 n forming) the control gate electrode CG are rounded. The reasonfor this is the same as the reason why the upper end corner portions C1and C2 of (the n type silicon film 4 n forming) the control gateelectrode CG are rounded when the silicon oxide film 9 a is formed inEmbodiment 1.

Namely, in Embodiment 1, in the cleaning step of Step S12, at thesidewalls of the lamination pattern 7, the insulation film 5 is sideetched. This results in the formation of the structure in which (sidesurfaces of) the insulation film 5 are retreated from (the side surfacesof) the control gate electrode CG and (the side surfaces of) theinsulation film 6. In this state, the formation step of the siliconoxide film 9 a (the oxidation treatment of the semiconductor substrate1) is performed. As a result, the upper end corner portions C1 and C2 ofthe control gate electrode CG are rounded. In contrast, in the presentembodiment, in the cleaning step of Step S10 a, at the sidewalls of thelamination pattern 7, the insulation film 5 is side etched. This resultsin the formation of the structure in which (the side surfaces of) theinsulation film 5 (are) is retreated from (the side surfaces of) thecontrol gate electrode CG and (the side surfaces of) the insulation film6. In this state, the sacrifice oxidation of Step S11 a (the oxidationtreatment of the semiconductor substrate 1) is performed. As a result,the upper end corner portions C1 and C2 of the control gate electrode CGare rounded.

In other words, the insulation film 5 is side etched, so that theinsulation film 5 is retreated from the control gate electrode CG andthe insulation film 6. As a result, not only the side surfaces of thecontrol gate electrode CG are exposed, but also the regions in thevicinity of the upper end corner portions C1 and C2 of the top surfaceof the control gate electrode CG are exposed. In this state, theoxidation treatment of the semiconductor substrate 1 (in Embodiment 1,the formation step of the silicon oxide film 9 a, in the presentembodiment, the sacrifice oxidation step of step S11 a) is performed.Accordingly, in Embodiment 1, at the stage of having formed the siliconoxide film 9 a, and in the present embodiment, at the stage of havingformed the sacrifice oxide film 8 in the step S11 a, the upper endcorner portions C1 and C2 of the control gate electrode CG are changedfrom the almost right-angled and sharp corner portions into the roundedportions.

Further, as with the cleaning step of Step S12 of Embodiment 1, alsowith the cleaning step of Step S10 a of the present embodiment, it ispreferable that L1 is equal to, or larger than T4 (i.e., L1≧T4), whereL1 denotes the length by which the insulation film 5 is retreated fromthe control gate electrode CG and the insulation film 6 at the sidewallsof the lamination pattern 7 due to side etching of the insulation film5, and T4 denotes the thickness of the silicon oxide film 9 a formingthe insulation film 9 formed in Step S13. Herein, the length L1 is shownin FIG. 34, and the thickness T4 is shown in FIG. 15. Further, it isfurther preferable that L1 is 4 nm or more (i.e., L≧14 nm), where L1denotes the length by which the insulation film 5 is retreated from thecontrol gate electrode CG and the insulation film 6 at the sidewalls ofthe lamination pattern 7. As a result, it is possible to furtherprecisely form the sufficiently rounded upper end corner portions C1 andC2 on the control gate electrode CG.

Further, in the present embodiment, in the sacrifice oxidation step ofStep S11 a, the exposed surfaces of the control gate electrode CG areoxidized. Thus, the upper end corner portions C1 and C2 of the controlgate electrode CG are rounded. For this reason, in order to allowprogress of oxidation of the exposed surfaces of the control gateelectrode CG, the sacrifice oxidation of Step S11 a is performed by theoxidation treatment of the semiconductor substrate 1, and preferably canbe performed by thermal oxidation. However, it is further preferablethat the step is performed by ISSG oxidation. Further, by the step offorming the silicon oxide film 9 a, the lower end corner portions of theinsulation film 6 also each become in the rounded shape.

Then, also in the present embodiment, the same cleaning treatment ofStep S12 (cleaning step) as that in Embodiment 1 is performed. FIG. 37shows an essential part cross-sectional view at the stage of havingperformed the cleaning treatment of Step S12 in the present embodiment.Further, FIG. 38 shows an enlarged view of the lamination pattern 7 andthe neighboring regions at the same stage as that of FIG. 37 (the stageof having performed the cleaning treatment of Step S12).

The cleaning treatment of Step S12 to be performed in the presentembodiment is basically the same as the cleaning treatment of Step S12performed in Embodiment 1. For this reason, also in the presentembodiment, as with Embodiment 1, using a cleaning solution containinghydrofluoric acid, specifically dilute hydrofluoric acid (an aqueoussolution of hydrofluoric acid), the cleaning treatment of Step S12 isperformed. Below, the cleaning treatment of Step S12 (cleaning step) tobe performed in the present embodiment is referred to as the cleaningtreatment of Step S12 a (cleaning step).

By the cleaning treatment of Step S12 a, as shown in FIGS. 37 and 38,the sacrifice oxide film 8 is etched and removed. Further, by thecleaning treatment of Step S12 a, it is possible not only to remove thesacrifice oxide film 8, but also to further side etch the insulationfilm 5 at the lamination pattern 7 in the memory cell region 1A.Therefore, the cleaning step of Step S12 a can also be regarded as theetching step.

By the cleaning treatment of Step S12 a, the sacrifice oxide film 8 isremoved. As a result, in the memory cell region 1A, portions of the mainsurface (silicon surface) of the semiconductor substrate 1 (p type wellPW1) not covered with the lamination pattern 7 (control gate electrodeCG), and the side surfaces (silicon surfaces of) the control gateelectrode CG are exposed. On the other hand, in the peripheral circuitregion 1B, the top surface (silicon surface) of the silicon film 4 isexposed.

In the cleaning treatment of Step S12 a, a cleaning solution containinghydrofluoric acid (preferably dilute hydrofluoric acid) is used. Forthis reason, the silicon film and the silicon nitride film are lesslikely to be etched than the silicon oxide film, and the semiconductorsubstrate 1, the n type silicon film 4 n, the silicon film 4, and theinsulation film 6 are hardly etched. These points are the same as withthe cleaning treatment of Step S12 of Embodiment 1.

Then, also in the present embodiment, the same formation step of theinsulation film 9 of Step S13 as that in Embodiment 1 is performed.

FIG. 39 shows an essential part cross-sectional view at the stage ofhaving formed the insulation film 9 of Step S13 in the presentembodiment. Further, FIG. 40 shows an enlarged view of the laminationpattern 7 and the neighboring regions at the same stage as that of FIG.39 (the stage of having performed the formation step of the insulationfilm 9 of Step S13). Incidentally, in FIG. 39, for facilitatingunderstanding of the drawing, the lamination film of the silicon oxidefilm 9 a, the silicon nitride film 9 b, and the silicon oxide film 9 cis simply shown as the insulation film 9. In contrast, in FIG. 40, theinsulation film 9 is shown as the lamination film of the silicon oxidefilm 9 a, the silicon nitride film 9 b, and the silicon oxide film 9 c.In actuality, the insulation film 9 is the lamination film of thesilicon oxide film 9 a, the silicon nitride film 9 b, and the siliconoxide film 9 c.

Also in the present embodiment, the configuration and the formationmethod of the insulation film 9 are basically the same as those inEmbodiment 1. Namely, also in the present embodiment, as with Embodiment1, the insulation film 9 includes the lamination film (ONO film) of thesilicon oxide film 9 a, the silicon nitride film 9 b, and the siliconoxide film 9 c sequentially formed from the bottom. As with Embodiment1, the insulation film 9 is, as shown in FIGS. 39 and 40, formed overthe surface of the p type well PW1 (however, the portions not coveredwith the control gate electrode CG), over the sidewalls (side surfaces)and the top surface of the lamination pattern 7, and over the topsurface of the silicon film 4 in the peripheral circuit region 1B.

In Embodiment 1 described above, in the silicon oxide film 9 a formationstep, by oxidizing the exposed surfaces (surfaces) of the control gateelectrode CG, the upper end corner portions C1 and C2 of the controlgate electrode CG were rounded. In contrast, in the present embodiment,by oxidizing the exposed surfaces (surfaces) of the control gateelectrode CG in the sacrifice oxidation step of Step Sila, the upper endcorner portions C1 and C2 of the control gate electrode CG are rounded.Accordingly, in Embodiment 1, the silicon oxide film 9 a formation stepis performed by subjecting the semiconductor substrate 1 to an oxidationtreatment, and is preferably performed by thermal oxidation (furtherpreferably ISSG oxidation). However, in the present embodiment, not onlywith these methods, but also with, for example, a CVD method, thesilicon oxide film 9 a can be formed. However, in the presentembodiment, when the silicon oxide film 9 a formation step is performedby subjecting the semiconductor substrate 1 to an oxidation treatment(preferably thermal oxidation, and further preferably ISSG oxidation),the exposed surfaces (surfaces) of the control gate electrode CG can beoxidized even in the silicon oxide film 9 a formation step. For thisreason, it is possible to further enhance the degree of roundness of theupper end corner portions C1 and C2 of the control gate electrode CGafter formation of the silicon oxide film 9 a as compared with beforethe formation of the silicon oxide film 9 a.

Further, at the sidewalls of the lamination pattern 7, the insulationfilm 5 is side etched, and is retreated from the control gate electrodeCG and the insulation film 6. Then, in Step S13, the insulation film 9is formed. Accordingly, in regions in which the insulation film 5 isretreated at the sidewalls 7 a and 7 b of the lamination pattern 7 (theregions corresponding to regions 30 c and 30 d shown in FIG. 38),portions of the insulation film 9 penetrate. The insulation film 9specifically includes a lamination film of the silicon oxide film 9 a,the silicon nitride film 9 b, and the silicon oxide film 9 c.Accordingly, in regions in which the insulation film 5 is retreated atthe sidewalls of the lamination pattern 7 (the regions corresponding tothe regions 30 c and 30 d shown in FIG. 38), portions of the siliconnitride film 9 b also penetrate.

The subsequent steps are the same as those in Embodiment 1. Namely, alsoin the present embodiment, as with Embodiment 1, the n type silicon film10 n for forming the memory gate electrode MG is formed in Step S14, andfurther, the steps subsequent to Step S14 are performed. However,herein, they are not shown, and a description thereon will not berepeated. Further, the structure of the manufactured semiconductordevice was described in Embodiment 1, and hence a description thereon isomitted.

In the present embodiment, almost the same effects as those inEmbodiment 1 can be obtained. In addition, the following effects canalso be obtained.

In Embodiment 1, by oxidizing the exposed surfaces (surfaces) of thecontrol gate electrode CG in the silicon oxide film 9 a formation step,the upper end corner portions C1 and C2 of the control gate electrode CGwere rounded. However, the film thickness of the silicon oxide film 9 ais required to be determined in view of the function as the gateinsulation film of the memory transistor. In contrast, in the presentembodiment, by oxidizing the exposed surfaces (surfaces) of the controlgate electrode CG in the sacrifice oxidation step of Step S11 a, theupper end corner portions C1 and C2 of the control gate electrode CG arerounded. However, the sacrifice oxide film 8 is removed at thesubsequent cleaning step of Step S12 a. Therefore, the film thickness ofthe sacrifice oxide film 8 can also be set large. The degree ofroundness of the upper end corner portions C1 and C2 of the control gateelectrode CG is affected by the oxidation rate when the exposed surface(surface) of the control gate electrode CG is oxidized (in Embodiment 1,the silicon oxide film 9 a formation step, and in the presentembodiment, the sacrifice oxidation step of Step S11 a). The larger theoxidation rate is, the larger the degree of roundness of the upper endcorner portions C1 and C2 of the control gate electrode CG tends to be.In the present embodiment, the degree of freedom for the oxidation rateof the sacrifice oxidation step of Step S11 a (corresponding to the filmthickness of the sacrifice oxide film 8) is high. The oxidation rate canbe set at the optimum value for rounding the upper end corner portionsC1 and C2 of the control gate electrode CG. This facilitates control ofthe degree of roundness of the upper end corner portions C1 and C2 ofthe control gate electrode CG.

On the other hand, after the cleaning treatment using hydrofluoric acid(in Embodiment 1, the cleaning treatment of Step S12, and in the presentembodiment, the cleaning treatment of Step S10 a or S12 a), a waterwashing treatment is necessary in order to sufficiently remove thehydrofluoric acid. In the present embodiment, after the cleaningtreatment of Step S10 a, and after the cleaning treatment of Step S12 a,the semiconductor substrate 1 is required to be washed with water(rinsed with water), respectively. In contrast, in Embodiment 1, afterthe cleaning treatment of Step S12, the treatment of washing (rinsing)the semiconductor substrate 1 with water is performed. However, in thecleaning treatment of Step S10, hydrofluoric acid is not used.Therefore, the hydrofluoric acid treatment and water washing steps ofStep S10 can be cut. Accordingly, the number of manufacturing steps ofthe semiconductor device can be reduced.

Up to this point, the invention made by the present inventors wasspecifically described by way of embodiments thereof. However, thepresent invention is not limited to the embodiments. It is naturallyunderstood that various changes may be made within the scope notdeparting from the gist thereof.

The present invention is effectively applicable to a semiconductordevice and a manufacturing technology thereof.

1-14. (canceled)
 15. A method for manufacturing a semiconductor device,the semiconductor device, comprising: a semiconductor substrate; a firstgate electrode and a second gate electrode formed over the top of thesemiconductor substrate, and adjacent to each other; a first gateinsulation film formed between the first gate electrode and thesemiconductor substrate; and a second gate insulation film formedbetween the second gate electrode and the semiconductor substrate, andhaving a charge storage part in the inside thereof, the method,comprising the steps of: (a) preparing the semiconductor substrate; (b)forming an insulation film for the first gate insulation film over themain surface of the semiconductor substrate; (c) forming a firstconductor film for the first gate electrode over the insulation film;(d) forming a first insulation film over the first conductor film; (e)forming a second insulation film over the first insulation film; (f)patterning the second insulation film, the first insulation film, andthe first conductor film, and forming a lamination pattern having thefirst conductor film forming the first gate electrode, the firstinsulation film over the first conductor film, and the second insulationfilm over the first insulation film; (g) side etching the firstinsulation film at a sidewall of the lamination pattern, and retreatingthe first insulation film from the first conductor film and the secondinsulation film; (h) after the step (g), forming a third insulation filmfor the second gate insulation film, and having a charge storage part inthe inside thereof over the main surface of the semiconductor substrateand the sidewall of the lamination pattern; and (i) forming the secondgate electrode adjacent to the lamination pattern via the thirdinsulation film over the third insulation film.
 16. The method formanufacturing a semiconductor device according to claim 15, wherein thefirst conductor film formed in the step (c) comprises a silicon film,wherein the first insulation film formed in the step (d) comprises asilicon oxide film, and wherein the second insulation film formed in thestep (e) comprises a silicon nitride film.
 17. The method formanufacturing a semiconductor device according to claim 15, wherein inthe step (g), by a wet treatment using hydrofluoric acid, the firstinsulation film is side etched.
 18. The method for manufacturing asemiconductor device according to claim 15, wherein the thickness of thefirst insulation film formed in the step (d) is larger than thethickness of the insulation film formed in the step (b).
 19. The methodfor manufacturing a semiconductor device according to claim 15, furthercomprising, after the step (f), and before the step (g), a step (f1) ofsubjecting the semiconductor substrate to an oxidation treatment, andforming a sacrifice oxide film, wherein in the step (g), the sacrificeoxide film formed in the step (f1) is removed, and the first insulationfilm is side etched.
 20. The method for manufacturing a semiconductordevice according to claim 15, wherein in the step (h), the thirdinsulation film comprising a lamination film having a first siliconoxide film, a first silicon nitride film over the first silicon oxidefilm, and a second silicon oxide film over the first silicon nitridefilm is formed.
 21. The method for manufacturing a semiconductor deviceaccording to claim 20, wherein when the first silicon oxide film isformed in the step (h), at a sidewall of the lamination pattern, thesurface of the first conductor film forming the first gate electrode isoxidized, and an upper end corner portion of the first conductor film isrounded.
 22. The method for manufacturing a semiconductor deviceaccording to claim 15, wherein the insulation film formed in the step(b) comprises a silicon oxynitride film.
 23. The method formanufacturing a semiconductor device according to claim 15, furthercomprising, after the step (g), and before the step (h), a step (g1) ofsubjecting the semiconductor substrate to an oxidation treatment, andforming a sacrifice oxide film; and after the step (g1), a step (g2) ofremoving the sacrifice oxide film formed in the step (g1).
 24. Themethod for manufacturing a semiconductor device according to claim 23,wherein when the sacrifice oxide film is formed in the step (g1), at asidewall of the lamination pattern, the surface of the first conductorfilm forming the first gate electrode is oxidized, and an upper endcorner portion of the first conductor film is rounded.